OJ - quick update. The global toggles per feature are now live in Charm 1.0.41, which just shipped via Sparkle.
You can now bind a keyboard shortcut to each of Charm's features (Spells, Polish, Oracle, and Emoji Replacement) and toggle them on or off from anywhere with a single keypress. Each shows a brief on-screen confirmation pill so you always know what changed and what state it's in. Set them up in Settings → Customise → Keyboard Shortcuts. All four default to unbound so you can pick whatever combos work best for you.
The per-app customisation side stays in the Customise tab as before, in case you ever want a feature on or off in specific apps.
On the tooltip-style emoji picker, that's a bigger UX project so it's on the list but not coming straight away. And the Slack backspace issue should still work around with Cmd+Z as I mentioned earlier.
Marking this one as complete. Thanks for the detailed write-up, it really helped shape the design. If anything else comes up just let me know.