3D Max - Can't apply new bones from lower body to an imported head with ready skinning

I’m trying to import a new head to another model with the scene merge option for Max, which already has bones as well as has already been skinned. I need to do this because the original head which belonged to the lower body had bad skinning done and the new one has much better skinning, and it’s also the same head as the old one. However, when I’m done attaching the vertexes of the new head to the old body and ready to add weights from the older bones to the new head (upper spine bone to influence the neck area of the new head), the vertexes of the new head move to the feet of the character, presumably following the pivot point of the head. I already tried moving the pivot points of the neck bone as well as the new head meshes but they still do this.

Is there any way I can fix this or do I need to remove the skinning from the new head, add the new bones and the required older bones and start over?

So let me understand this. Are you trying to combine two meshes and keep their respective skin weights fully intact? If so there’s quite an easy way to do this with Skin Wrap.

Basically, I have two meshes, a head and a lower body. They both have their own unique skeletons but I want to attach the newer head skeleton to the older skeleton which is on the lower body. Adding the new head and neck bones to the lower body and skinning them to the lower body works just fine but if I add any of the bones from the lower body to the new head and weight any vertex from the head with those bones, the vertexes retreat back to the origin point where the head got originally imported to the scene, no matter if i move the normal and skin pivot points of the head related meshes and skeleton to the area where the neck bone and the lower body meet.

And I want to keep the head and lower body as separate meshes.

1.) Before beginning any operations, select the body mesh (BODY) and go to Skin -> Advanced Options and toggle Always Deform. If the mesh moves in any, then reload the save file and instead do 1b. Otherwise, proceed to 2.

1b.) Right-click the Skin and choose Copy. Then right-click the skin and choose Collapse To. You now have only an Editable X, with no Skin modifier. Right-click above the Editable X, and choose Paste. This will paste the Skin back on. The mesh might move when you do this, that’s fine. Once again, toggle Always Deform. If your mesh moved, it will now have snapped into its correct place.

2.) Do Step 1, but this time for the HEAD mesh.

3.) Link the bones as you wish. The Always Deform / Skin Copy should prevent the mesh from moving around as you link things.