- if it has one (which is posible, maybe to give it that wet, slimmy shine the rakghouls have), just erase it, replace it with a uniform dark gray as above, afterwards write "cm_baremetal" (no quotation marks) on a note pad or word pad text file, then rename it to file extension .txi and drop it on the override along with the texture with the edited alpha channel.
That's not exactly right. To make texture transparent, you don't need cm_baremetal OR ANY OTHER envmaptexture in the *.txi. In most cases you don't need *.txi at all, or you may need to make a blank *.txi.
Also, you'll need to check appearance.2da. Look for the envmap column for your appearance. If it's value is DEFAULT - everything is OK, if not - change it to default and it sould work fine.
EDIT: just checked TSL rakghoul texture.
You'll need to edit alpha-channel like Capibara said, and *.txi file should look like this:
Remember, that *.txi file name must be exactly like the name of the texture.