Well I pulled on the vent cover, held my breath, pulled a little harder and...POP, the cover was in my hand. Screws hold the cover base in place (4) and managed to leave them in tact. I did this in the bedroom and was surprised to see that styrofoam ducting continues beyond the vent towards the closet. I'm thinking of sticking some closed cell foam in the dead space to block off the superfluous ducting.