Building instructions are on GitHub;
You would want to modify Electron.hx to pull each respective API from new source.
If you don't (e.g. just run index.html on a web server), GMEdit will work in "lite" mode where it only loads a pre-defined set of plugins (see PluginManager) and opens/saves project ZIPs or YYZs.
Since you did not identify the specific problems nor what you want to use as a replacement, that's all I have.