I am sure that people have changed out keels....but why?
On my boat, which is a 34' shoal draft, the keel weighs 5,200 pounds. Anyone price 5,200 pounds of lead formed into a keel with bolts lately? There are way to many boats out there for sail to get into this kind of a refit.
With new rudder, probably in the neighborhood of $20,000. Buy one with the keel you want!