My 17 y/o Granddaughter shoots with me, is a lefty, and understands the concept of eye dominance. She has chosen to shoot righty. She says it's so she can shoot nearly all rifles.
Once the muscle memory is up and running normally, she's a righty whenever she's operating a firearm.
When I was in 3rd grade, I received a pretty serious collection of fractures to my right hand; and it was in a cast so long, it required me to learn how to live life as a lefty for quite awhile. When the cast came off, I found that I was, to a moderate extent, ambidextrous. Most of that has worn off over nearly 60 years, but I still find myself doing things righty and/or lefty unconsciously. Baffles me, too. I guess some of that muscle memory stuck...
My older Brothers taught me a bit about boxing. They noticed I had a natural tendency to switch between left and right handed stances, and built on that. Sometimes I think that part was harder for them than it was for me. Later, when I did some formal intramural boxing in the Service, switching stances sometimes gave me a small edge.
It's not just about muscle memory, IMHO. There's something going on with me that I don't understand. I do the eye dominance test on myself, and sometimes it comes out I'm right eye dominant and sometimes it's left eye dominant. Beats me, but it also seems that maybe eye dominance is not a 'cast in concrete' constant. I do know that university researchers have used special glasses to flip images upside down, which also reverses the left/right eye configurations. After a day or two, the test subjects resumed their activities and reported they could see as normal. Once the glasses were removed, they reverted back to their original visual orientation in a fraction of the time it took to accommodate the special glasses. My conclusion is that eye dominance and visual orientation are learned things, and can be retrained and reoriented, maybe more easily than many think.
Being able to do that kind of reversion increases the number of opportunities available to the individual.
Greg