I am not taking pred any longer. I went off it 17 years ago and to be honest it took me a year to wean off it. I was take 60 mg and weaned off very slowly and under a Dr's care, make sure you do this under Dr's care!
As for plastic surgery, I have not had any done but I have had back and shoulder surgery a few years back and it had no effect on my MG {but I was in remission at that time} There are always risks with surgery so just make sure it is something you really want before doing it.
When you come off the pred I am sure you will start feeling better about yourself and the surgery may no longer be needed or wanted.
Keep us updated on how you are doing