Kicking balls get into the game all the time. Most big schools rotate balls on EVERY play, so you simply make sure the ball boy knows which ball to rotate in on 4th down.
As long as it is an APPROVED ball, no big deal.
As for the actual ball, it is NOT underinflated, if anything, it's over inflated. An underinflated ball won't go as far. Part of the force of the kick is the trampoline effect, the ball compressing on the foot and rebounding from that compression. An underinflated ball will not rebound as well. Of couse, a ball inflated like a rock won't compress to begin with, so the rebound effect is also minimized.
And punters and holders don't want a slick ball either, they have to catch it too. In fact, a slick ball is very hard on a holder, who has to grab that ball with his hands while it is travelling very fast. A punt returner cradles the ball against his body and doesn't rely as much on his hands alone, so the slickness isn't that big of an issue.
The BIG advantage of a "kicking ball" is that the seams have been cracked, or broken in. A new ball has a bladder seam that runs right down the spine of the ball. When a ball is new, the bladder seam as well as the leather seams are still "tight", and again, that trampoline effect is minimized. Once these seams are cracked, or "broken", the ball compresses more, and therefore rebounds more off the foot.
So the only thing a kicker wants is a ball that is properly to slightly overinflated, and is broken in. Many of these balls meet all of the requirements of rule 1-3.