COACHING CAROUSEL MOD
So you can kind of make a coaching carousel.
At the end of the season, say, after the NT game, you can go into COCH table in your save file, and set every FBS team's CFUC to 1. This sets every coach as a user coach.
Then go back in the game, and change "fire" coaches manually.
The game will then auto-populate the coach from the pool of available head coaches (mostly from FCS).
So, one idea is to make a "free agent" pool of coaches in the FCS.
You can also, at this point, take the fired coaches, which will now show as "NO TEAM", and try to put them on teams that will want to hire them as well.
After this is done, you can save, and then go back into your COCH table and remove the CFUC from all the CPU teams.
To set this up, ahead of time, I would recommend changing all the FCS coach names and ratings to whoever you want, so when the teams hire new coaches, it's all set-up.
I have tried this in NCAA 07 on PSP, and it worked beautifully. Some of the changes that happened:
Texas Tech hired Kellen Moore
UCLA hired Alex Grinch from USC
Virginia hires Deion Sanders
and so on...
The other thing to note is that the "fired" coaches are swapped with the "hired" coaches, so they become part of the free agent pool for the next time you do this.