Welcome to ribnet!
Thing with outboards is the market (compared to cars) is miniscule, hence not designing everything "bespoke". There are plenty ways to "de tune", as you say, a restrictor gasket, hard stops on the throttle mechanism, even different cams on the spark advance follower (Older machines the throttle advances the spark - the throttle is generally driven off that)
Newer machines, when you look at the relatively small market & cost differences, you can kind of see why they might want you to buy the bigger engine to get your extra gee gees! Have a trawl through the forums here - you will quickly find who resprayed what into their own livery, and what might be easily re-powered. Some it;s a siomple djustement, others you might as well buy the bigger engine by the time you have replaced the parts!
Thing with EFI is there is also a compooter to re-tune too.... What's yours hanging on? You may find 25 is plenty!
Pop back with Qs once you've had a search- plenty of opinion on here, average it out & you'll get a reasonable answer!
(use "advanced" to keep it to the engine forums - Loco knows a fair bit about the Tohatsus