Hey there!
I’m a little confused by the post, so I’ll just run through the process I use here and if it doesn’t answer your question, just let me know which area specifically sounds like the area you’re running into issues!
Character Creation Process:
-Setup skeleton settings
-Place skeleton in mesh
-Paint skin weights (if you had no model at this point and used the proxy, you skip this for now)
-Build Control Rig
Now let’s assume you didn’t have your model yet, and now you do, so you can go to Epic Games → Edit Existing Character → select the character you want and hit edit export file.
Now you can import your mesh, and start binding it to your skeleton. If all you do is skin weighting, there will be no need to rebuild the rig, as long as you make sure the file gets saved with the model in rig pose (in the UI, reference pose manager → assume rig pose)
For some clarification on the two files that get created, the export file houses the joint mover, your mesh, and your skin weighting. The rig file is what gets built from the export file (it makes a new scene, references in the export file, and then builds the rig on top of that). All edits to joint placement, skin weighting, etc, are done in the export file.
Let me know if I can clear anything else up. From your post, I got the impression that you had already built a control rig, but hadn’t yet skinned the model fully or were maybe using the proxy geo?
Thanks!