When you create a twitch channel they automatically generate an emote prefix for your channel sub emotes. For example, if your channel is called billygames your prefix could be "billyg6" then add the name of your custom emote at the end eg billyg6hi. 

Twitch's current stance on emote prefix changes URL

FAQ - Can I change my Sub Emote prefix?

"Partners can inquire about a different Sub Emote prefix by contacting us via https://www.twitch.tv/help We are not allowing changes to Affiliate sub emote prefixes at this time."

WHY?

For those of us that created our twitch channel names to be a representation of our birth names, this is a problem. Especially when we legally change our name and our twitch channel name as well. For instance, if a trans person created their twitch channel with their birth name and then decide to transition - they have no way to change their emote prefix and remove their deadname unless they get partnered. This can cause massive dysphoria that is crippling for them.

This is a ridiculously un-inclusive move on twitches side and it's time that they update their stance on this. Will you sign to make a change?