diff --git a/Wabbajack.Lib/AInstaller.cs b/Wabbajack.Lib/AInstaller.cs
index c2833ea1..6c8d7512 100644
--- a/Wabbajack.Lib/AInstaller.cs
+++ b/Wabbajack.Lib/AInstaller.cs
@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.IO.Compression;
 using System.Linq;
+using System.Windows.Navigation;
 using Wabbajack.Common;
 using Wabbajack.Lib.Downloaders;
 using Wabbajack.VirtualFileSystem;
@@ -160,6 +161,9 @@ namespace Wabbajack.Lib
                     File.Move(from, to);
                 else
                     File.Copy(from, to);
+                // If we don't do this, the file will use the last-modified date of the file when it was compressed
+                // into an archive, which isn't really what we want in the case of files installed archives
+                File.SetLastWriteTime(to, DateTime.Now);
             }
 
             vFiles.GroupBy(f => f.FromFile)
@@ -285,5 +289,40 @@ namespace Wabbajack.Lib
             File.WriteAllText(cache, e.FileHash());
             return HashArchive(e);
         }
+
+        /// <summary>
+        /// The user may already have some files in the OutputFolder. If so we can go through these and
+        /// figure out which need to be updated, deleted, or left alone
+        /// </summary>
+        public void OptimizeModlist()
+        {
+            Utils.Log("Optimizing Modlist directives");
+            var indexed = ModList.Directives.ToDictionary(d => d.To);
+
+            indexed.Values.PMap(Queue, d =>
+            {
+                // Bit backwards, but we want to return null for 
+                // all files we *want* installed. We return the files
+                // to remove from the install list.
+                var path = Path.Combine(OutputFolder, d.To);
+                if (!File.Exists(path)) return null;
+
+                var fi = new FileInfo(path);
+                if (fi.Length != d.Size) return null;
+                
+                return path.FileHash() == d.Hash ? d : null;
+            }).Where(d => d != null)
+              .Do(d => indexed.Remove(d.To));
+
+            Utils.Log($"Optimized {ModList.Directives.Count} directives to {indexed.Count} required");
+            var requiredArchives = indexed.Values.OfType<FromArchive>()
+                .GroupBy(d => d.ArchiveHashPath[0])
+                .Select(d => d.Key)
+                .ToHashSet();
+            
+            ModList.Archives = ModList.Archives.Where(a => requiredArchives.Contains(a.Hash)).ToList();
+            ModList.Directives = indexed.Values.ToList();
+
+        }
     }
 }
diff --git a/Wabbajack.Lib/MO2Compiler.cs b/Wabbajack.Lib/MO2Compiler.cs
index 9aa041d1..b13e67da 100644
--- a/Wabbajack.Lib/MO2Compiler.cs
+++ b/Wabbajack.Lib/MO2Compiler.cs
@@ -305,7 +305,7 @@ namespace Wabbajack.Lib
         private void BuildArchivePatches(string archive_sha, IEnumerable<PatchedFromArchive> group,
             Dictionary<string, string> absolute_paths)
         {
-            using (var files = VFS.StageWith(group.Select(g => VFS.Index.FileForArchiveHashPath(g.ArchiveHashPath))).Result)
+            using (var files = VFS.StageWith(group.Select(g => VFS.Index.FileForArchiveHashPath(g.ArchiveHashPath))))
             {
                 var by_path = files.GroupBy(f => string.Join("|", f.FilesInFullPath.Skip(1).Select(i => i.Name)))
                     .ToDictionary(f => f.Key, f => f.First());
diff --git a/Wabbajack.Lib/MO2Installer.cs b/Wabbajack.Lib/MO2Installer.cs
index 0620cfb4..3658ba1a 100644
--- a/Wabbajack.Lib/MO2Installer.cs
+++ b/Wabbajack.Lib/MO2Installer.cs
@@ -3,6 +3,7 @@ using System.IO;
 using System.Linq;
 using System.Text;
 using System.Windows;
+using System.Windows.Forms.VisualStyles;
 using Wabbajack.Common;
 using Wabbajack.Lib.Downloaders;
 using Wabbajack.Lib.NexusApi;
@@ -17,6 +18,8 @@ namespace Wabbajack.Lib
 {
     public class MO2Installer : AInstaller
     {
+        public bool WarnOnOverwrite { get; set; } = true;
+        
         public MO2Installer(string archive, ModList mod_list, string output_folder)
         {
             ModManager = ModManager.MO2;
@@ -52,7 +55,7 @@ namespace Wabbajack.Lib
             Directory.CreateDirectory(OutputFolder);
             Directory.CreateDirectory(DownloadFolder);
 
-            if (Directory.Exists(Path.Combine(OutputFolder, "mods")))
+            if (Directory.Exists(Path.Combine(OutputFolder, "mods")) && WarnOnOverwrite)
             {
                 if (MessageBox.Show(
                         "There already appears to be a Mod Organizer 2 install in this folder, are you sure you wish to continue" +
@@ -66,6 +69,7 @@ namespace Wabbajack.Lib
                 }
             }
 
+            OptimizeModlist();
 
             HashArchives();
             DownloadArchives();
@@ -99,6 +103,7 @@ namespace Wabbajack.Lib
             return true;
         }
 
+
         private void InstallIncludedDownloadMetas()
         {
             ModList.Directives
diff --git a/Wabbajack.Test/ACompilerTest.cs b/Wabbajack.Test/ACompilerTest.cs
index 4197ad33..fd86133e 100644
--- a/Wabbajack.Test/ACompilerTest.cs
+++ b/Wabbajack.Test/ACompilerTest.cs
@@ -57,6 +57,7 @@ namespace Wabbajack.Test
         {
             var modlist = MO2Installer.LoadFromFile(compiler.ModListOutputFile);
             var installer = new MO2Installer(compiler.ModListOutputFile, modlist, utils.InstallFolder);
+            installer.WarnOnOverwrite = false;
             installer.DownloadFolder = utils.DownloadsFolder;
             installer.GameFolder = utils.GameFolder;
             installer.Begin().Wait();
diff --git a/Wabbajack.Test/SanityTests.cs b/Wabbajack.Test/SanityTests.cs
index fc49e42a..22f2485a 100644
--- a/Wabbajack.Test/SanityTests.cs
+++ b/Wabbajack.Test/SanityTests.cs
@@ -55,6 +55,55 @@ namespace Wabbajack.Test
             utils.VerifyInstalledFile(mod, @"Data\scripts\test.pex.copy");
         }
 
+        [TestMethod]
+        public void TestUpdating()
+        {
+
+            var profile = utils.AddProfile();
+            var mod = utils.AddMod();
+            var unchanged = utils.AddModFile(mod, @"Data\scripts\unchanged.pex", 10);
+            var deleted = utils.AddModFile(mod, @"Data\scripts\deleted.pex", 10);
+            var modified = utils.AddModFile(mod, @"Data\scripts\modified.pex", 10);
+
+            utils.Configure();
+
+            utils.AddManualDownload(
+                new Dictionary<string, byte[]>
+                {
+                    { "/baz/unchanged.pex", File.ReadAllBytes(unchanged) },
+                    { "/baz/deleted.pex", File.ReadAllBytes(deleted) },
+                    { "/baz/modified.pex", File.ReadAllBytes(modified) },
+                });
+
+            CompileAndInstall(profile);
+
+            utils.VerifyInstalledFile(mod, @"Data\scripts\unchanged.pex");
+            utils.VerifyInstalledFile(mod, @"Data\scripts\deleted.pex");
+            utils.VerifyInstalledFile(mod, @"Data\scripts\modified.pex");
+
+            var unchanged_path = utils.PathOfInstalledFile(mod, @"Data\scripts\unchanged.pex");
+            var deleted_path = utils.PathOfInstalledFile(mod, @"Data\scripts\deleted.pex");
+            var modified_path = utils.PathOfInstalledFile(mod, @"Data\scripts\modified.pex");
+
+
+            var unchanged_modified = File.GetLastWriteTime(unchanged_path);
+            var modified_modified = File.GetLastWriteTime(modified_path);
+
+            File.WriteAllText(modified_path, "random data");
+            File.Delete(deleted_path);
+
+            CompileAndInstall(profile);
+
+            utils.VerifyInstalledFile(mod, @"Data\scripts\unchanged.pex");
+            utils.VerifyInstalledFile(mod, @"Data\scripts\deleted.pex");
+            utils.VerifyInstalledFile(mod, @"Data\scripts\modified.pex");
+
+            Assert.AreEqual(unchanged_modified, File.GetLastWriteTime(unchanged_path));
+            Assert.AreNotEqual(modified_modified, File.GetLastWriteTime(modified_path));
+
+
+        }
+
 
         [TestMethod]
         public void CleanedESMTest()
diff --git a/Wabbajack.Test/TestUtils.cs b/Wabbajack.Test/TestUtils.cs
index abb10136..f39e95d3 100644
--- a/Wabbajack.Test/TestUtils.cs
+++ b/Wabbajack.Test/TestUtils.cs
@@ -182,6 +182,11 @@ namespace Wabbajack.Test
             }
         }
 
+        public string PathOfInstalledFile(string mod, string file)
+        {
+            return Path.Combine(InstallFolder, "mods", mod, file);
+        }
+
         public void VerifyAllFiles()
         {
             foreach (var dest_file in Directory.EnumerateFiles(InstallFolder, "*", DirectoryEnumerationOptions.Recursive))
diff --git a/Wabbajack.VirtualFileSystem/Context.cs b/Wabbajack.VirtualFileSystem/Context.cs
index 0eba5c69..2137ce7d 100644
--- a/Wabbajack.VirtualFileSystem/Context.cs
+++ b/Wabbajack.VirtualFileSystem/Context.cs
@@ -139,7 +139,7 @@ namespace Wabbajack.VirtualFileSystem
                 {
                     var magic = Encoding.ASCII.GetString(br.ReadBytes(Encoding.ASCII.GetBytes(Magic).Length));
                     var fileVersion = br.ReadUInt64();
-                    if (fileVersion != FileVersion || magic != magic)
+                    if (fileVersion != FileVersion || magic != Magic)
                         throw new InvalidDataException("Bad Data Format");
 
                     var numFiles = br.ReadUInt64();
@@ -223,7 +223,7 @@ namespace Wabbajack.VirtualFileSystem
             }
         }
 
-        public async Task<DisposableList<VirtualFile>> StageWith(IEnumerable<VirtualFile> files)
+        public DisposableList<VirtualFile> StageWith(IEnumerable<VirtualFile> files)
         {
             return new DisposableList<VirtualFile>(Stage(files), files);
         }