I read swapping regular aliens for spitters and almost had a heart attack ! As for swapping meshes, given how UE4 works I imagine that you still need to recompile everything as the ubuk is its own esoteric thing. Albeit when you look at the popular mod for enhancing the two stupid synths it is actually only 14kb so there must be a way to swap easily. The main issue everyone wanting to mod the game has is the utter lack of any guide while at the same time UE modding is messy as hell to begin with.