I'm not quite sure what you are after, ie I don't know where you want the icons, I've done my best to tell how to use them in 2.3.
In prefixes you can use this in extra.less for before and/ or after, e.g. with the lightGreen prefix:
	
	
	
		Code:
	
	
		.label.label--lightGreen {
  
  
    &:before {
        .m-faContent(@fa-var-flower-tulip);     
    }
    &:after {
        .m-faContent(@fa-var-flower-daffodil);      
    }
}