I believe it is not a violation for the consumer to overpower a boat over that of its suggested HP max. In an accident, there could be liabilty however. For an OEM boat builder, i believe there are HP guidelines.

I know folks purchase hull and trailer combos and power their boat after the fact in some cases. This is fairly common in higher elevations over 4000 feet as the loss of horspower affects performance. Something we see later and from the "usual" locales.