Model part replacement (Trouble copying weights/skin partition)

[Warhawk72482]

I'm trying to replace a certain model part with another for a personal mod. I've followed the directions I've found in numerous places, but nothing seems to work.

All of the directions state to copy bone weights (It SEEMS to work, until I open up the exported file in NifScope), and they say to Build Skin Partitions, but I don't see that option anywhere in Outfit Studio.

 

I've tried to do a New Project and use the original body part as the reference, and then imported the new model (as both .obj from Blender and a .nif).

 

When I do so, I get the following message:

The reference shape has a skin coordinate system that is different from the global coordinate system. Would you like to copy the reference's global-to-skin transform to the imported shapes?

 

 

Then, when I try to export the new model as a nif, I get the following error:

The following shapes have unweighted vertices, which can cause issues. The affected vertices have been put under a mask. Do you want to save anyway?

 

The body part I am trying to replace is for a power armor suit (the bodysuit, specifically)