Re: Converting
I am surprised the dealer won't convert it for you, just take the motor off and tell him you would like it goosed up to the 115hp level, he should have no problem with that. That said
Now on the safety side, many boats I have seen can take more that what they are rated for, but you better make sure everything is in perfect shape, they are rated for a certain HP for a reason, based on structure and design and then certified for that, you also might want to check the liability laws in the state you reside in, in the state I live in, if I put more on the transom that what the boat is rated for, I can be ticketed and god forbid if I have an accident with injuries, watch out, because I can be charged with a felony and do prison time!
In all honesty and it is just my opinion, it would probably be cheaper in the long run to pick up a boat rated for the type of HP you want to run..but again, that is just my opinion, I am sure others will be different..