Since Santy Anna is in the refrain, it was easy for him to "win the day," particularly among British and other singers who had no idea who General Taylor was, no reason to care, and no pedantic motive to keep his name in the song.

While there was no slavery in Mexico, Santa Anna was a dictator widely loathed by the Mexican public. The idea that replacing Taylor with Santa Anna in the shanty was some kind of "political statement" strikes me as wildly improbable - especially since a *politically minded* innovator would have known that Taylor won.

And no collected verses refer to slavery in Mexico or the U.S.