Yes it is possible? There is a chance it could be converted simply by drilling out the orifice, but that would depend on what kind of valve it uses. If not, you would probably have to find a valve from someone that wants to make the switch from NG to LP and would just swap with you. Otherwise, finding a NG valve from one being junked would be the other possibility.
If you want to explore the first avenue of modifying the orifice, I am not the one to talk to. Hopefully, someone else will be able to guide a bit better on that.