This is designed for Slack >= 4.22
Run either setup for the BEEEEEG version or setup-beeeg-E-smolz for the BEEG version or setup-smol for the smol version. If you're running macOS then it will help you by installing Homebrew and Node.js
This method is unlikely to work because of the permissions needed to modify the Slack application files.
Install an extension
https://chrome.google.com/webstore/detail/slack-beeegmojis/hggahljepmkkbfbgfddldbaflncchgpm
https://addons.mozilla.org/en-US/firefox/addon/slack-beeegmojis/
https://microsoftedge.microsoft.com/addons/detail/dmeboaaoabeepmjadgaokkmkgoakkdib
If you want to use the BEEEEEG version then you'll need to use an unpacked extension.
Run the setup script with -u to return Slack back to stock.
Raise a PR