Shari, I've been coping with MG since the 1970's. What I've always done is work a little, rest a little. I've never had any long term trouble out of resting the affected muscles, then going back to doing the same thing. Although the 2nd or 3rd time around I am not able to do nearly as much before fatiguing, and usualy eventually have to quit for the day. But the next day I can be right back at it.
One trick I learned years ago is to mix up my tasks. That is, do a little of one thing, then do a little of something else that uses different muscle groups, or even the same muscles, but in a different way. That way, I am able to accomplish more before I have to take a break.
Interesting thread, I'm glad you brought it up, and I'll look forward to the hints the others have.
Hugs,