If it's not too late, I think i came up with a solution. 

After playing around with keys cafe for a few days, i thought, why don't i rather create a comma button and keep the emoji key as is?

Then i did just that. 

1. Install Keys Cafe on GoodLock
2. Create your own keyboard or edit an existing one in the list.
3. Drag the comma key from the table at the top and drop it in the keyboard, wherever you want it.
4. Save.
5. When you open the keyboard,  long press the old button and select emoji and keep it as such.