For those using the free ChatGPT web UI, I've made a free browser extension/addon that will allow you to maintain and switch between multiple custom instruction sets, so you can give ChatGPT different contexts/personalities at the press of a button:
https://github.com/tf318/chatgpt-custom-instruction-switcher
You can install it in Firefox from the Add-Ons store: https://addons.mozilla.org/en-US/firefox/addon/chatgpt-instr...
It's still under review for the Chrome Web Store, so for now for Chrome/Edge you can follow the sideloading instructions at the GitHub URL.