Ask, and you shall receive!
I wanted to be able to add a Micro.blog emoji to my profile at Mastodon.Social. The administrators at another instance had done that in the past (thank you!), but I decided to stay at the _mother_instance in the end. So I asked @Eugen if he could do it, and literally 5 seconds later he had added the emoji to the list. Thanks!
Fellow Micro.bloggers, if you want to add it to your profile, or use it in conversation, :microblog: is now available! Yay!