yes, as said by Steve, the idea is to do many sets throughout the day, each set way below what you could have done. I´m greasing the groove at the office with door frame pull ups, to work finger and pulling strength. This is how I have structured it:
- The first day I tried my max, which was 4 pull ups.
- every time I go to pee or to the kitchen, I do 1 set of 2 pull ups (so 50% of my max). I end up doing about 7 sets of 2 reps throughout the day.
Under this scheme, I think it is ok to do another exercise between sets. As a matter of fact, The Naked Warrior, which is based on GTG, consists on 2 exercises: pistol squats and one arm push ups. So to your original question, of doing presses or rows between squat sets, my answer would be: yes.