One way is easy the other harder. First is the prop just a pp2 file or does it have an object file as well? If it has an object file, meaning the pp2 references on external object file, it is easy. Just map the object and save it over the old object, or rename it and edit the pp2 with a text editor to the new object. You will find the object inside. Use the find function for .obj to make sure you get them all, then save the pp2 under a new name. If it has embedde geometry, then I am lost. Someone posted here a tutorial on making props point to external objects that might help you edit the pp2 to point to your object and include the morphs. I don't have that and could not find the prop in free stuff to look myself.