If you rename "BAT Mod 2.1" to "BAT Mod 2.0" you'll trick BTS into thinking you have 2.0 installed. You'll need to rename the existing 2.0 folder out of the way, first. I'm pretty sure 2.0 and 2.1 are saved-game compatible, but be forewarned that there have been many reports of crashes when loading games with 2.1, so you may want to wait a bit until we can settle it.
If you want to try 2.1 anyway, you should be able to reverse the trick later to continue under 2.0.