Last week I happened to catch the part of the Toledo/Akron game to see this situation happen. Akron's starting left tackle goes down to injury, and so now they have to move their tight end, #49, to take his place. They change his jersey number to #59 and properly report to the referee, but the number on the side of his helmet still says #49. Is there a provision in the rules making this permissible or is it just one of those things you have to decide on a case-by-case basis?