Why do you want to drop those exercises? Do they hurt in a bad way? Is there something else you think is more effective?
I would ask the PT what the purpose is for those exercises, and ask for alternatives that you can tolerate, or ask if you can drop them out. Or else I would just make an executive decision and not do them. I'm not sure how much help a bunch of strangers on the internet can be when it comes to rehab in a specific individual.
Personally, I'm not a fan of tricep extensions nor leg extensions- they put weird stresses on my elbows/knees for minimal results, but maybe that's because I haven't done them since my knee was busted up and I was trying to rehab it. The best thing I ever did for my knee was squatting- bodyweight at first, then under a bar.