Hi @thecaptain,

Sure it's possible via CSS code. See the example below:

#wpforo #wpforo-wrap #wpforo-menu li:first-child:before {
    font-family: "Font Awesome 5 Free";font-weight: 900;content: "\f007";
}
#wpforo #wpforo-wrap #wpforo-menu li:nth-child(2):before {
    font-family: "Font Awesome 5 Free"; font-weight: 400; content: "\f1ea";
}

The CSS codes should be added in the "Custom CSS code" textarea, located in the Dashboard > Forums > Settings > Style Tab.  

Please don't forget to delete all caches and press Ctrl+F5 (twice) on the frontend before checking to reload the updated CSS file.