Although I haven't seen the changelog for the "b" version, it is likely a bugfix, as it has been before. By applying a mod based on a previous "a" version of the game, you'll be effectively downgrading your game completely or partially from "b" to "a", potentially still dealing with the bugs that have been already fixed in the "b" or creating brand new ones.
Depending how the mod has been built, you may also disable the "extended" part of the game.
Obviously, you can experiment and see for yourself. Just keep the "0.97b extended" zip file around to be able to revert to the unfucked unmodded original game.