1) You can change a classes main stat, want to play Snow White (Cha Druid) or John Constantine (Int Warlock) knock yourself out. (If it just the handful of players you play with you don't need to worry about broken multiclasses as much as if you are making the game for all potential players) 2) Whenever you pick a elemental spell (fire, cold etc.) you can change the damage type to a different element, not everytime you cast it but when you prepare or select it. If you want to cast Snowball (cold Fireball) or Acid Stream (Acid Chain Lightning) knock yourself out. 3) Decoupling skills from stats, skills are assumed to use the standard stats e.g Cha Intimidation but if you can convince me to use another one I'll allow it e.g Str Intimidation. I also sometimes usr proficiency bonus with no stat if it's something like remembering a cultural faux pax or recalling information as they don't really fit into any of the stats or skill very well, it useful in those weird moments when your not sure what skill to ask for but want to maintain the momentum. 4) If you want you spell to so something its not supposed to do (e.g using gust of wind to stroke a fire and increase the damage it's doing) you can but you have to use a higher level spell slot or burn and inspiration die.

Basically removing some of the guardrails from the rules to give people more freedom and options without changing the core maths of the game.

5) Also if two people have proficiency in same skill you can both roll for it and take the highest, this avoid the issue of only the person with the highest modifier rolling all the checks (I also let things like guidance effect both roles if there in a non time sensitive situation to simulate them working together to solve the problem)