Boats, like bedrooms are there for you to do with as you will. You can decorate them, extend them, rebuild
them, whatever it takes to make it a great place to be. But you do have to consider the effect such a modification will have on a boat's performance.
By adding a 3' scoop, we extended our boat from 40' to 43'. The original hull wasn't touched, it was simply an extension. However, it altered the stern shape. Rather than the transom being a flat drop into the water
, which used to cause all sorts of eddies (read resistance whilst racing), the rounded stern now slips through the water
nicely, and the boat moves faster.
If considering a boat which has had major modification, it's important to get it surveyed, and to sail it in a variety of conditions to assess how the modifications have affected performance.