Hello! That's an interesting thought... it's not currently possible without actually editing the scripts (you'd need to add extra arguments to the setup script to give the alternative(s) to use, plus the "weight" for each one, then edit the ADD scripts to pick the tileset used based on this weight). HOWEVER, I do think it's an excellent Idea! I'll be working on this over the coming weekend and I'll see about adding in such a functionality. Thanks!