It says: As long as the school does not mandate that it is absolutely necessary to say "itadakimasu", I think that protesting is a mistake. Or more simply, "As long as the school does not forcibly require (students) to say "itadakimasu" ..." かぎり means "as long as" and is followed by a verb either in the affirmative or the negative present or past tense: 食べるかぎり -> as long as I eat 食べないかぎり -> as long as I don't eat 食べた限り -> as long as I ate 食べなかった限り -> as long as I didn't eat