There isn't really much to it, though... some mice have physical designs that favour right handed people.
Assuming you're using Xorg 7.. as per the xf86-input-mouse man page I can't locate in FreeBSD.
- Place the mouse on the left side of the keyboard..
- Edit your current /etc/X11/xorg.conf file, or generate a new one.
- Add Option "ButtonMapping" "3 2 1" to your Mouse0 section.
Other options exist for Xorg <= 6, most require a .Xmodmap file.. which would still work, I'll let that be a Google exercise for you.
