Is there any sort of pet addon that allows me to set rules for when an ability can be used? I just want to make it so my scorpid will only use claw when he has 50 or more focus, to leave himself enough focus to use scorpid poison whenever it cools down.

I think this functionality was broken. There used to be a pretty comprehensive pet behavior addon (Servitude) that covered all warlock pets and I think some hunter pet behavior as well, and that one was broken most definitely.

Servitude page at curse gaming
http://wow-en.curse-gaming.com/downloads/details/883/

This function was most defiantly broken.