Customizing a prefix is important as an affiliate building an accessible community by not having it, Twitch is creating systemic exclusion. The community members who need to type out the emoji instead of clicking it will be used to typing out an emoji by name and, if you cannot change the prefix until you are a Partner, you are punishing the creator's community--because by customizing it after the community is built (i.e. after you are Partner) then you forcing a bunch of Twitch viewers who type in emojis to have to relearn a new prefix because what they are comfortable with is no longer a valid prefix
Customizing a prefix is important as an affiliate building an accessible community by not having it, Twitch is creating systemic exclusion. The community members who need to type out the emoji instead of clicking it will be used to typing out an emoji by name and, if you cannot change the prefix until you are a Partner, you are punishing the creator's community--because by customizing it after the community is built (i.e. after you are Partner) then you forcing a bunch of Twitch viewers who type in emojis to have to relearn a new prefix because what they are comfortable with is no longer a valid prefix