I can’t speak authoritatively, but, the rule says he can’t change position - it doesn’t say he can’t be substituted.
But, now the question becomes, if a sub enters the game, does he have to assume the snapper’s position? Or, may another player move to snapper and the sub take another poisition?
The real question is why? I never had an opportunity to ask Dave Nelson, John Adams or Redding why this rule existed. But, no rules ‘scholar’ I have asked had an answer, much less a good answer. But, it has to go back to a time with wing Ts, leather helmets, and horns instead of whistles for officials.
Robert