I understand one can overtrain players putting some of those 4 variants to 10, BUT if I got an injured QB for some 3-4 weeks shouldn't I be able to put him on 10 on GameTapes ?
Not sure if you picked game tapes meaning only for your next opponent or overall understanding your whole playbook. Of course other position players should do well too with this.

An injured player hardly can get overtrained by watching game tapes to learn your system better. Even better if it's a freshman that needs to sit out on the other training sessions. One create a training schedule with only 10 on game tapes.
Or am I thinking outside the box ?

I don't think there is an issue with putting a 10 in any category... where you get overtraining is when you put more than 20 points total in the schedule since the player won't have time or energy to do everything.