Having migrated a few, I don’t see why youd have any issues migrating to source build providing the engine version is the same.
In fact, most of them just ended up opening and working directly with a few nasty exceptions.
I guess the question is what kind of mod are you expecting to be produced.
A whole level needs different kind of access than creating a custom asset, for instance.
You can take a page from Ark - they tell you get the engine, and here is how you produce stuff and here is where you place it in the game folder.
At a base level - all mods - are tied to the executable of the game reading the contents of a folder and making use of them.
You can write this in c++ in under 10 minutes.
How you use what contents you read, that’s a deeper discussion. If it’s literally just a mesh, and correlated textures, you could even go as far as hot loading an FBX and the textures into a material instance dynamic.
If you wanted to create an internal tool, that’s a different story…