Hold down the heart to set your own reactions.
Discussion
hold down the heart.
good album or song title.
I can add emojis doing as you suggest, but when I go to select for use, they are not visible. I'm on Android if it matters.
It should let you just use your phone keyboard to enter the emoji the same way you would when typing a post
Logic would dictate, but I can only do that within a post. When I long press the heart beneath a post to "react" to it, I get what you see in the screenshot. The bottom list of emojis are animated, which is not what I want. 
New reaction symbol.
(It'll bring up your keyboard)
Enter the emoji you want.
Save.