Final Fantasy Hacktics

As the title suggests in wondering about utilizing Jp boost on concert with innate jp boost, meaning that i would add the innate boost to all classes, and leave it as a support ability. Would they stack? Cancel each other out, create a zero-sum mass in my hands that would end the world?

Thanks for any response!

Subject says it all, im looking for anyone who might know when jobs and sprite sets in the game are safest for modding, i used simon to create my own Cinder Knight (yes he is as cool as he sounds). But i dont know what other sprits and characters i can safely high-jack for my own nefarious purposes.

If anyone knows off-hand which are most suitable i would appreciate it. Thank you for your time!