RTF is a global modification that replaces all towns in the game.

I've calculated the stats, now I'll work on the building tree.

Yes, you really do calculate everything quickly :)

Added 12 minutes later
In general, I looked around a bit, and it seems you can adjust the city building options in the "Shared" settings. I didn't delve too deeply, I replaced the peasant building with goblins and then put everything back the way it was.