LinuxMint

If you login in terminal, add the following line into ~/.xinitrc before "exec i3":

xmodmap -e "pointer = 3 2 1"

If you login with Xfce GUI, add above line into ~/.xsessionrc.

If you want to change to right-hand style mouse buton, run the following command in console:

xmodmap -e "pointer = 1 2 3"

Ref: https://askubuntu.com/questions/151819/how-do-i-swap-mouse-buttons-to-be-left-handed-from-the-terminal