Pulseaudio - Swap L/R channels

Edit file /usr/share/pulseaudio/alsamixer/profile-sets/default.conf

Look for the relevant section, similar to this:

[Mapping analog-stereo]  
device-strings = front:%f hw:%f  
channel-map = left,right

Change the order from "left, right" to "right,left". A restart of the service might be required: pactl exit