When are my “previously unalterables” still unalterable?

I’m asked a lot about the “previously unalterable” provisions: those sections of a society’s constitution which must be moved into the bylaws and may be altered by a special resolution of the membership after the society transitions. But some societies are not at liberty to change these, at least not without ministerial permission. Others may put their funding or charitable status at risk if they modernize their bylaws.