Bill Lake is a decently successful boxers, and a righty. For whatever reason, his coach thinks he should learn to box as if he was a lefty. Could he learn to do it as well as a naturally left-handed person? Or at all?
Michael Moorer did that. Became heavyweight champion by defeating Evander Holyfield to win the title. However, in his first defense he was knocked out by “Big” George Foreman. Many southpaws converted to a conventional stance because other boxers avoided fighting a southpaw.
Not strictly boxing but Bruce Lee advocated positioning your strongest side forward, leading with a straight right punch. (As well as switching leads when advantageous.) I’m reasonably tall, and got a lot out of a (relatively) quick, strong right lead and right leg snap kick. Maybe my left cross and left roundhouse that followed weren’t as strong as my right side woulda been, but it was just about different ways to combine the same tools.
I never minded fighting guys with unmatched leads. Just created different opportunities. But I would suspect most pro boxers would prefer matched stances.
Could a boxer learn to be as good a lefty as a naturally left-handed boxer? (Sorry, I somehow erased my OP).
Yes. There’s nothing special about fighting from a southpaw stance except that it’s tougher on your opponents. Everybody is used to fighting righthanders so even lefthanders don’t want to fight lefthanders.
A boxer’s dominant hand isn’t necessarily their best weapon. Many righthanded boxer’s best weapon is their left jab.