Editing skeletal meshes is a question which occasaionally comes up and I didn't have a dedicated video for it. The process is mostly covered in my skeletal rigging video, but this is more of a step by step guide.

In this video the stick-rifle of the US Ranger is replaced with something a little higher in poly count. Which is what most people seem to want to do. No changes are made to the skeleton or animation. The new mesh is linked to existing bones.