The previous version of BottomScanner allowed for custom baserules. I was using the one stickied in the tuning forum, but this option seems to have been replaced with a GUI config window. But the stickied baserule, which was working great btw, seemed to have a lot of options that the GUI config window doesn't support.
Instead of a baserule, you can write "evaluator modules" which do much the same thing as baserules but in a tidier, more efficient and extensible way. You can have more than one module active at a time, listed by priority in BtmScan.toc, and configure each one through the UI. Take a look at Eval*.lua in the BtmScan directory for examples. EvalTemplate.lua is a skeleton with comments explaining how to add your own.
Be sure to do as Chardonnay notes and take a look at the Eval*.lua file, instructions are in there about how to create new Evaluators. The format is different given the extra options in Evaluators, but if you come up with something cool, please post it for us or add it to the Evaluators wiki, it's currently empty.
Evaluators are for Auc5, though BtmScan seems to work somewaht with Auc4, I've had issues trying to use it alone with it (without the rest of Auc5 installed), as a FYI.