when you change lens do you...

unlock only, since that way one of my hands becomes free to do whatever else i need to (i.e. unscrew the cap of the other lens)

Actually, now that I think of it:

1. Turn camera body face down with right hand.
2. Grab lens with left hand.
3. Push release button with left thumb.
4. Twist lens (thereby sliding thumb off release button). <-- Answers OP's question
5. Put lens down.
6. Move rear lens cap from new lens onto old lens.
7. Attach new lens to body.
8. Point, shoot, enjoy.

Phew... I have no idea why I know all of this detail.

Take a look at the lens mount and the lens. Once the pin has been pulled back and the lens rotated slightly, the pin slides on the steel lens ring.

Just as it does when you mount a lens. Do you hold the button down when doing that? Same thing...

-js