I have been handquilting for about 40 years. I long ago trained myself to use both hands. Since I touch type and play the piano it was not as hard since both actions use both hands equally.
I find I only do it when I am using a stationary quilting frame. If I am using a small handheld hoop I just turn the hoop around rather than use the opposite hand. I have more problems with the computer now than quilting. Using the mouse can lead to a very aching right arm. I have both carpal tunnel in both hands and an autoimmune disease that makes my muscles in general weak. Since I find hand quilting relaxing it is almost therapy for me. My hands bother me the most when I have used the rotory cutter or iron. I have the new Martini ergonomic cutter. It does help. I tend to do a lot of tearing of my fabrics as it assures a straight line but that makes my upper arms ache. I also hate the strings that result.