I would go with what your surgeon recommends. I asked mine about any special exercises before my reverse TSR last year, and he said no.

If your arm is painful enough to be thinking of shoulder replacement, it's probably bone on bone along with arthritis and very restricted movement of that arm. Chances are you have already gone through PT for a simpler solution and it has not given much relief. In order to build or improve muscle fiber you have to work it to past a point of discomfort so the muscle has a reason to thicken. The problem is that your point of severe pain from your bone on bone will prevent you from even getting your muscle up to it's point of discomfort, so all you'll have is pain without any gain.
Shoulder replacement has a very different schedule from knee replacement. With knees, they want you up and walking and moving as much as you can immediately. With shoulders, you wear an immobilizer sling day and night for up to 6 weeks. You do not start PT at once, when and what depends on whether you had a regular or a reverse procedure. You may do two or more daily sessions of various arm pendulum swinging exercises which only keep the rotational channel of your new joint working well, but don't involve any muscle activity. So any new muscle which you thought to build in the weeks before surgery will probably fade away due to enforced inactivity of that arm for the next month.
Again, I suggest checking with your doctor or surgeon.