Adding any emoji as a reaction remains under review.
I am marking this as partially done to let you know a new reactions bar with Like, Heart, Laugh, Surprised, Sad, and Angry has begun rolling out to all users.
An error occurred while saving the commentHassan Gulzar commented
I'd also like a configurable reaction emoji set. I want to be able to react to my Face-Palm chat message emoji with a face-palm reaction. It is needed.