Yes, you can also use different icons for different categories. You can use separate line for separate category in the bottom of the style.css file like
.category-faq .fa-file-zip-o::before, .category-faq .fa-file-archive-o::before { content: '\f0f1' !important; }
where faq is the Category Slug. You can find the Slug from WP-Admin > Posts > Categories
