Because of the construction techniques used, I think that most modern charter
cats do not lend themselves to significant changes to the layout once built. Of course anything is possible if you have enough money
and time, but I suspect the choice of an ex-charter cat as a starting point does not indicate a surfeit of the former.
You an do limited things like changing the use of a WC/shower stall to say a wet locker or laundry
or repurposing a cabin
as a workshop, but moving even non structural bulkheads while retaining a decent appearance in keeping with the rest of the boat
Perhaps it would help if you could give some idea of the changes you think you would need to make.