So, you have decided that you do not like the name of your PhantomBot. Things happen, maybe you changed the vibe of your stream or you just looked at the name one day and wondered what you were thinking.
Here is how you go about changing the name of the bot:
First, register the name of the account on Twitch like you did the first time with the name of the bot. Then, while logged in as that account, go to https://twitchapps.com/tmi/ and acquire a new OAuth Key. Edit the botlogin.txt file and change the user= setting to the name of the new account you created, also change the oauth= setting to the new key that you obtained from the TwitchApps website.
Note that Twitch highly recommends enabling two-factor authentication on any bot accounts. It would be a great idea to do so at this time. Remember that a bot has moderator access to your channel and the more secure you can make that account the better.
Note that you do not need to re-register your Twitch Account with PhantomBot and generate a new API Oauth key. That key is tied to your Twitch streaming account and not your bot account.