Hello, I'm wondering whether it's possible to change the web UI of Mattermost. For instance, if I want to add new effects or change icons of files/chats, etc., can it be done? If yes, does it involve recompilation? I understand that Mattermost uses React as the front-end, and I have no experience in it or is it possible to change views directly on an installed version?
I'm okay even if the answer is too broad and tells me to "go learn React first". 
But I'd really appreciate some guidance here.