mouse side button configuration

I have a Microsoft Intellimouse and just recently discovered that the side
buttons do something. They work as forward and backwards buttons in web
I found a number of articles and threads on how to get the side buttons to
work, but came up short on finding out how to change what the buttons do.
I’d like to use them as copy and paste. The middle mouse button is something
I never could get used to using for that, but for many years I used these
mice with windows and set the side buttons for copy and paste - and got used
to it.
How are the settings changed regarding what the mouse buttons do?


I usually use xbinkeys to accomplish this.