It's definitley possible to add custom icons to the footer of your store. If you wanted some help with it, depending on which theme your using there are a few different ways to go about it.
If you're on a free Shopify developed theme then you can contact the Shopify support team and someone from theme support can look into helping you. You're eligible for 60 minutes of free design time if you're also on a paid Shopify plan.
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