Cannot change existing block's icon

Hi all, great JS plugin btw! Im new to programming and i would like to know a few things:

editor.BlockManager.get('map').set({
	attributes: {
		class: 'fa fa-heading'
	}
});

I want to set the icon as a "heading" icon from font awesome but it not doing it and its not throwing any error.

thanks to everyone for all the help and great plugin!