^If you do what I did and source a pair of older [pre 2005.5 model year] version buttons , not easy as they are quite rare, and your setup is like mine:
My setup is an RCD510, midline clocks, no bluetooth so obviously the left hand buttons don't do anything. But the right hand set let me:
1. Switch radio stations or tracks if listening to MP3s on SD card with the left and right buttons [as opposed to up/down on the newer buttons.]
2. Adjust the volume.
There is a mute button on the left hand button set but it doesn't work, I suspect it might work with bluetooth.
NOTE: If you try to do this with the newer buttons and a midline display cluster it WON'T WORK!