Eets mods are possible, just really hard
Honestly, I'm surprised it even wanted to read the extra files I injected into it.
Cobbled something together to make modding marginally easier, but it's still real jank, and I'm not even sure if it works outside of my testing environment (requires Java and Python3, Build 2: patch non-functional patch postfix): https://unownfo.s-ul.eu/XYpgCsOf
1. Place folders in archive on root of Eets install (where uninstall is)
2. Run Decompile.bat to (try to) decompile the game [if game was installed in an admin folder, run as admin]
3. Run Eets.bat to (try to) do a full recompile of the game [if game was installed in an admin folder, run as admin]
Eets arbitrary code execution ("DunkinDonuts.etr") demo (unsandboxed LUA execution from malformed replay, due to game using non-proprietary packing format that's easily replicated): https://unownfo.s-ul.eu/p7YT3lmD
Description of the ACE sounds scary, but:
1. Unzip a replay with any ZIP file unzipping tool (change extension to .zip if necessary)
2. Run a LuaC to Lua decompiler on "replay.etr" (I used unluac.jar)
3. Add as much code as you want
4. Compile the replay back to LuaC (I used luac50, it's old enough to support this game, *ensure it's under the name "replay.etr"*)
5. Zip the files back into a new .etr file (the custom level .eet file *must* be first when you look at the ZIP file in the hex editor, EMP [see above] contains its own .zip merging Python script to help with the issue, I'd say use 7z 4.57 for this (doesn't contain extra headers to gunk up the file size))