The question is addressed to Neil but I take the opportunity to answer. The modifications of this type as the day hatch is very easy, especially if you add comercial hathes. You must add third bulkhead and open up a hole.
You 're not change stractual part of the boat, instead this you add reinforcement with the bulkhead, unless you use minicell foam. This period of time i modify the foredeck of my boat to give more space to my feet. Generally the modifications are possible to these parts.
You must be more careful if you want to modify the hull or structural parts of the boat, like the bulkhead, the carlines, the stringers and so.
I must except from the above mentioned, the strip build, or pvc foam core, nomex core boats that they achieves the stiffness of the structure by joining the hull and deck.
You 're not change stractual part of the boat, instead this you add reinforcement with the bulkhead, unless you use minicell foam. This period of time i modify the foredeck of my boat to give more space to my feet. Generally the modifications are possible to these parts.
You must be more careful if you want to modify the hull or structural parts of the boat, like the bulkhead, the carlines, the stringers and so.
I must except from the above mentioned, the strip build, or pvc foam core, nomex core boats that they achieves the stiffness of the structure by joining the hull and deck.