There are certainly some manufacturers that have glassed in components after they're installed. It's insane. However, I would approach your problem from that perspective. How did they install it in the first place? Does the sink come out?
You may end up cutting an access port, you can fill them with a deck access port, or make or have made a door that matches the rest. This is not exactly a common boat so it may be hard to find anyone with this exact experience. Photos might help. One advantage of making an access port is that you may gain a bit of storage, and that is always a good thing.