Some good ones in there. I do some of those already, especially the recruiting rules. I agree that it's a great way help manage the challenge level.
I think I may adopt your historic jersey number tradition. I like that one.
Also, I just implemented a new one last weekend similar to your "Give a random player a big attributes increase/decrease between seasons". I became dissatisfied how many of my players just felt generic, and did not stand apart much from one another. I wanted to do something to mix in a "Clowney" type of freak that comes along every few years, or at the very least, a noticeably better freshman than typical. (Amari Cooper, for example)
Here's the details on mine:
I haven't decided the frequency of this, but last class I randomly drew 2 incoming freshmen and did my own "Gem" or "Bust". For my Gem, I get to add 25 attribute points anywhere I want, however there's a max of +5 to any one skill. For my Bust, I have to deduct 25 attribute points (5 points in 5 key skills). The deductions have to be relevant to that player's position (can't take away -5 on punt power for a WR, that doesn't matter)
The results my first trial was interesting. The Gem +25 randomly fell on a 4* DE, who was already a cpu gem. So, this 4* came to Tuscaloosa rated 81 (+7 cpu gem), then the result of my Gem +25, which added +4 more = an 85 rated Freshman to spice things up! My Bust was a 4* MLB that fell from a 79 over to a 75.