There is a lot that goes into the determination of max HP. I don't know all but length, width, construction, and strength of the transom are some of the things. That tag in your boat is a federal requirement and they are suppose to be in all power boats. While you probably could get away with a bigger motor, I would strongly advise against it. If you were ever involved in an accident and it was found out, you could be hung out to dry. Not to mention your insurance company would not have to honor your policy. I also know that you could be disqualified in some tournaments.
Fair Winds and Following Seas
Bill H. PTC USN Ret
Chesapeake, Va