Since you've added the FA code in the navBarItems template. You can designated different icons by using CSS.
When you inspect in google chrome, firefox, or whatever browser you use. A little tedious work, add these in your custom.css
[data-navitem-id="87"] .fa-comment:before {
content: "\f206";
}
For each icon inserted, change the ID of the navitem-id and change the content: "\f206" to your prefer icon number.