KTM 390 Adventure Part 33 (EBC double H sintered brake pad upgrade) 

I've always deglazed using green scotch brite pads and a little brake cleaner and scrubbed the rotor. No reason sand paper wouldn't also work but probably a little more aggressive than is necessary.

You have to pull the nipple through the tab and turn it all the way up with the small crank, then an arrow appears immediately and you press on it and the door for the brake pads opens. I'm only joking. 😁

Have you ever tried planish grinding with a mill and rotary table on the tiny disc's?