Why not? It’s fairly easy to change the mold, lay up before anything. If the molds start full length it’s easy to take inches off the back with the use of clay.
Your need different molds, been down this road. You can't just shorten the hull without adding some width to the hull, short narrow hull rides like garbage.
As for making a cheap quality ski, that's cool and all, but the only place you can cut cost will be your labor rate. So if you dont mind making pennies for all your time invested, your be good to go.
Imo hull needs to be infused, if you dont know how to do that, I'd definitely get the equipment and learn how, well worth it.
As for skis that sale, an all around slightly shorter hull (-6/-10") and flatwater hull (-12+")seem to be the most popular skis right now, since there is no more surf events, surf hulls aren't as popular as they use to be.