Numbering question.

[Illini_Ref]

I had a local HS coach approach me at a local restaurant today while I was eating lunch (so much for being anonymous). He coaches at a very small school with limited numbers of kids.

He wanted to know if he could line up his FB on the line as an interior lineman(his number is <50). I told him that was fine as long as there were seven ont he line and at least five was numbered 50-79. Evidently that wouldn't be the case. He asked if he had a number in the 50s if he could run the ball, I said yes, but he wasn't an eligible receiver. Now my question (and I should know this). Can a kid change jerseys during the game for reason of numbering?