Making parts of textures invisible in an editor

[Robititties]

Hey all, did you know there was a cool mask underneath the Big Hat armor in DS3?

 

Well I want to erase the hat but I only remembered how to edit targa-to-png files from Dark Souls: PtDE and, needless to say, that doesn't work the same way with .dds files. I converted to BC3_unorm as suggested by the iGP11 readme, but I don't really know what I'm doing wrong from there when I edit them in a similar fashion, particularly about the bump mapping. Everything turns out black and splotchy when I edit the files in real-time, or just after rebooting the game

 

Any advice/corrections/help would be appreciated