UV Maaping and Mark Seams in Blender?

[Soulslayerzx]

Figured this would be a more appropiate section to post questions about blender.

 

So I edited some helmet from skyrim, I removed some parts, added new ones too. I use the texture meant for the vanilla mesh, some parts fitted well, others didn't.

 

When I select everything, there's a uv map that looks like the vanilla texture, but if I hit u and select unwrap, it looks different. I think this has something to do with the seams and I don't know what edges Bethesda cutted to mark the seams. So, do I just copy, paste, rotate, resize, and edit? Or is there a way to add on to the vanilla texture and texture the missing parts in the original texture, highly unlikely? lol.

[Soulslayerzx]

Anyone?