diff --git a/FrostyModSupport/Mod/ModUpdater.cs b/FrostyModSupport/Mod/ModUpdater.cs
new file mode 100644
index 00000000..2f41433f
--- /dev/null
+++ b/FrostyModSupport/Mod/ModUpdater.cs
@@ -0,0 +1,209 @@
+using Frosty.ModSupport.Mod.Resources;
+using Frosty.Sdk;
+using Frosty.Sdk.DbObjectElements;
+using Frosty.Sdk.IO;
+using Frosty.Sdk.Managers;
+using Frosty.Sdk.Utils;
+
+namespace Frosty.ModSupport.Mod;
+
+public class ModUpdater
+{
+    public enum Errors
+    {
+        Success = 0,
+        InvalidMods = -1,
+    }
+    
+    private static Dictionary<int, HashSet<int>> s_bundleMapping = new();
+    
+    public static Errors UpdateMod(string inPath)
+    {
+        (BaseModResource[], Block<byte>[], FrostyModDetails, uint)? mod;
+
+        string extension = Path.GetExtension(inPath);
+
+        if (extension == ".daimod")
+        {
+            // TODO: daimod convert
+        }
+        else if (extension != ".fbmod")
+        {
+            return Errors.InvalidMods;
+        }
+        
+        using (BlockStream stream = BlockStream.FromFile(inPath, false))
+        {
+            // read header
+            if (FrostyMod.Magic != stream.ReadUInt64())
+            {
+                stream.Position = 0;
+                mod = UpdateLegacyFormat(stream, inPath.Replace(".fbmod", string.Empty));
+            }
+            else
+            {
+                mod = UpdateNewFormat(stream);
+            }
+        }
+
+        if (mod is null)
+        {
+            return Errors.InvalidMods;
+        }
+        
+        FrostyMod.Save(inPath, mod.Value.Item1, mod.Value.Item2, mod.Value.Item3, mod.Value.Item4);
+
+        foreach (Block<byte> block in mod.Value.Item2)
+        {
+            block.Dispose();
+        }
+        
+        return Errors.Success;
+    }
+
+    private static (BaseModResource[], Block<byte>[], FrostyModDetails, uint)? UpdateNewFormat(DataStream inStream)
+    {
+        uint version = inStream.ReadUInt32();
+        
+        long dataOffset = inStream.ReadInt64();
+        int dataCount = inStream.ReadInt32();
+
+        if (ProfilesLibrary.ProfileName.Equals(inStream.ReadSizedString(), StringComparison.OrdinalIgnoreCase))
+        {
+            return null;
+        }
+        
+        (BaseModResource[], Block<byte>[], FrostyModDetails, uint) retVal = default;
+        retVal.Item4 = inStream.ReadUInt32(); 
+        
+        retVal.Item3 = new FrostyModDetails(inStream.ReadNullTerminatedString(), inStream.ReadNullTerminatedString(),
+            inStream.ReadNullTerminatedString(), inStream.ReadNullTerminatedString(), inStream.ReadNullTerminatedString(),
+            version > 4 ? inStream.ReadNullTerminatedString() : string.Empty);
+        
+        int resourceCount = inStream.ReadInt32();
+        BaseModResource[] resources = new BaseModResource[resourceCount];
+        for (int i = 0; i < resourceCount; i++)
+        {
+            ModResourceType type = (ModResourceType)inStream.ReadByte();
+            (int, string, Sha1, long, int, string, IEnumerable<int>) b;
+            BaseModResource.ResourceFlags flags;
+            switch (type)
+            {
+                case ModResourceType.Embedded:
+                    b = ReadBaseModResource(inStream, version);
+                    resources[i] = new EmbeddedModResource(b.Item1, b.Item2);
+                    break;
+                case ModResourceType.Bundle:
+                    b = ReadBaseModResource(inStream, version);
+                    inStream.ReadNullTerminatedString();
+                    int superBundleHash = inStream.ReadInt32();
+                    // TODO: update hash and add bundle hash to s_bundleMapping
+                    
+                    resources[i] = new BundleModResource(b.Item2, superBundleHash);
+                    break;
+                case ModResourceType.Ebx:
+                    b = ReadBaseModResource(inStream, version);
+                    flags = AssetManager.GetEbxAssetEntry(b.Item2) is not null ? BaseModResource.ResourceFlags.IsAdded : 0;
+                    
+                    resources[i] = new EbxModResource(b.Item1, b.Item2, b.Item3, b.Item4, flags, b.Item5, b.Item6, b.Item7, Enumerable.Empty<int>());
+                    break;
+                case ModResourceType.Res:
+                    b = ReadBaseModResource(inStream, version);
+                    flags = AssetManager.GetResAssetEntry(b.Item2) is not null ? BaseModResource.ResourceFlags.IsAdded : 0;
+                    
+                    resources[i] = new ResModResource(b.Item1, b.Item2, b.Item3, b.Item4, flags, b.Item5, b.Item6, b.Item7,
+                        Enumerable.Empty<int>(), inStream.ReadUInt32(), inStream.ReadUInt64(),
+                        inStream.ReadBytes(inStream.ReadInt32()));
+                    break;
+                case ModResourceType.Chunk:
+                    b = ReadBaseModResource(inStream, version);
+                    flags = AssetManager.GetChunkAssetEntry(Guid.Parse(b.Item2)) is not null ? BaseModResource.ResourceFlags.IsAdded : 0;
+
+                    uint rangeStart = inStream.ReadUInt32();
+                    uint rangeEnd = inStream.ReadUInt32();
+                    uint logicalOffset = inStream.ReadUInt32();
+                    uint logicalSize = inStream.ReadUInt32();
+                    int h32 = inStream.ReadInt32();
+                    int firstMip = inStream.ReadInt32();
+                    
+                    IEnumerable<int> superBundlesToAdd = Enumerable.Empty<int>();
+                    if (flags.HasFlag(BaseModResource.ResourceFlags.IsAdded))
+                    {
+                        // TODO: add to superbundle
+                    }
+
+                    resources[i] = new ChunkModResource(b.Item1, b.Item2, b.Item3, b.Item4, flags, b.Item5, b.Item6,
+                        b.Item7, Enumerable.Empty<int>(), rangeStart, rangeEnd, logicalOffset, logicalSize, h32,
+                        firstMip, superBundlesToAdd, Enumerable.Empty<int>());
+                    break;
+                default:
+                    throw new Exception("Unexpected mod resource type");
+            }
+        }
+        
+        return retVal;
+    }
+
+    private static (BaseModResource[], Block<byte>[], FrostyModDetails, uint)? UpdateLegacyFormat(DataStream inStream,
+        string modName)
+    {
+        DbObjectDict? mod = DbObject.Deserialize(inStream)?.AsDict();
+        if (mod is null)
+        {
+            return null;
+        }
+
+        return default;
+    }
+
+    private static (int, string, Sha1, long, int, string, IEnumerable<int>) ReadBaseModResource(DataStream inStream, uint version)
+    {
+        (int, string, Sha1, long, int, string, IEnumerable<int>) retVal = default;
+
+        retVal.Item1 = inStream.ReadInt32();
+
+        retVal.Item2 = (version < 4 && retVal.Item1 != -1) || version > 3 ? inStream.ReadNullTerminatedString() : string.Empty;
+
+        if (retVal.Item1 != -1)
+        {
+            retVal.Item3 = inStream.ReadSha1();
+            retVal.Item4 = inStream.ReadInt64();
+            inStream.Position += 1; // we discard the flags and just check with the AssetManager if the asset was added
+            retVal.Item5 = inStream.ReadInt32();
+            retVal.Item6 = version > 2 ? inStream.ReadNullTerminatedString() : string.Empty;
+        }
+        
+        // prior to version 4, mods stored bundles the asset already existed in for modification
+        // so must read and ignore this list
+        if (version < 4 && retVal.Item1 != -1)
+        {
+            int count = inStream.ReadInt32();
+            inStream.Position += count * sizeof(int);
+
+            count = inStream.ReadInt32();
+            HashSet<int> bundles = new(count);
+            for (int i = 0; i < count; i++)
+            {
+                int hash = inStream.ReadInt32();
+                bundles.UnionWith(s_bundleMapping[hash]);
+            }
+            retVal.Item7 = bundles;
+        }
+
+        // as of version 4, only bundles the asset will be added to are stored, existing bundles
+        // are extracted from the asset manager during the apply process
+        else if (version > 3)
+        {
+            int count = inStream.ReadInt32();
+            HashSet<int> bundles = new(count);
+            for (int i = 0; i < count; i++)
+            {
+                int hash = inStream.ReadInt32();
+                bundles.UnionWith(s_bundleMapping[hash]);
+            }
+            retVal.Item7 = bundles;
+        }
+        
+        return retVal;
+    }
+}
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