There is no codes code unfortunately, you have to manually go in and change every one of them separately.
To get the other HB's more carriers you'll need to sub them into the FB1 position.
If you are actually playing the team I usually go in substitutions and change their lineup around so that the different HB's and DE's get reps.
To adjust the coaches you'll need to go into the coaches options and change everything there.
For auto assists I put the Owner Mode on CPU and leave the rest on HUM until the free agency so the CPU doesn't cut plays thinking they are a waste of money. At free agency Ill change all the teams I don't wanna control to CPU and then proceed as normal.
After the new season begins I'll change the auto assist back to HUM except Owner mode.
Yes I play with injuries on. I just finished my 2020 season and Baltimore lost the Superbowl to NO because Lamar Jackson had gotten injured in the AFC Championship game and couldn't play.
Injuries are a good thing to keep on.