Permanent files (as compared to "normal" files) are designed to be more permanent by nature. Even if they have triggers, they're meant to reinforce changes, so that you become more and more like what's in the file's description. Theoretically, by the time you listen to a permanent file long enough, you'll fully feel like the animal/whathaveyou that's in the description (Even though, realistically, nobody really gets that far and your brain will snap out and default back to human outside of trance). Trigger/normal files by default are more "temporary", so that you can have fun being a cat/fox/etc for a day, but can turn back into a human (or default furry) whenever you're done having fun.
So, typically, it doesn't matter what the induction is.....but the file itself usually doesn't include a way to go back to human (either you revert by the end of a time period, or there's a trigger back)....and usually the file focuses on reinforcing changes.