Adding bowsprits is not for the timid. By and large the addition of one after the fact isn't worth the actual cost but it is no way impossible. I think you need a real engineer
to to really examine and compute this all out and not some Internet
Adding a 3 ft extension for some frivolous thing is no big deal but for what you are thinking about it needs to be computed properly. These are big numbers you are dealing with and the thickness of the sprit is maybe the least of the problems. All the attachments and how this is connected matter a whole lot too. The details here are quite important.
All the real success stories I have heard all lead me to think it's one of those more money
than brains adventures - and that is when it works. It generally adds little to the basic performance of the boat.