anytime you hit the cueball with anything else then your cuetip, it's a foul. Ferrule, shaft, butt, doesn't matter.
Now you will see people just tap their end of the shaft on a ball in the pack or something, but they are taking a foul, so they can hit it with whatever they want, it just ends up being a foul, but that's what they wanted.
That type of rule, I would think would be pretty universal in all games, in most places. Bottom line is, you can play whatever rules you want to, but you should both be in agreement with them ahead of time.
That could be a spot though.. one person has to make all balls with his the butt of his cue, or his shaft only, or the other end of the shaft only, or the butt, but he has to use the screw sticking out to cue with.