MacOS Theming Toolkit
If you are on a version above El Capitan you MUST disable SIP. Do so by entering Recovery Mode. Heading to Utilities > Terminal and running csrutil disable.
Start by running:
curl -o- https://macthemes.co/mti-setup.sh | bash +x
This will install the easy_mount command to your system along with necessary things for MTInstaller to work. Next you will need to run sudo easy_mount. This will remount your system for the current uptime. You need to run easy_mount after every reboot if you want to change the theme again. Themes DO persist through reboots however.
Shoutout to the dev behind FileIcon this tool makes this whole toolkit possible!