Not so subtle. No, it's not legal. On 1,2 or 3rd down, only the snapper can use the numbering exception in a scrimmage kick formation. On 4th down, all linemen can use the exception in a scrimmage kick formation.
Here's the subtlety. The numbering exception on 1st, 2nd, or 3rd down applies only to the field goal formation (as in 2-14-2a), not the punt formation (2-14-2b). So if the punt team comes on to the field on 1st, 2nd, or 3rd down, they must have legal numbering.
(7-2-5)
ART. 5 . . . Player formation and numbering requirements include:
a. At the snap, at least seven A players shall be on their line of scrimmage.
b. At the snap, at least five A players on their line of scrimmage must be numbered 50 to 79.
EXCEPTIONS:
1. On first, second or third down, when A sets or shifts into a scrimmage-kick formation
as in 2-14-2a, the snapper may be a player numbered 1 to 49 or 80 to 99. If Team A has the snapper in the game under this exception, Team A shall have at least four players wearing numbers 50 to 79 on its line of scrimmage.