MacOS – Any way to edit and/or add autocorrect entries

For specific terms you find are getting "corrected" often, you could add them to the text substitution list as substitutes of themselves. That should work as a sort of whitelist to stop them from being autocorrected improperly.

Open up the Language & Text panel in System Preferences, and on the Text tab, click the + to add a new substitution. Enter the word you want whitelisted into both fields.

My workaround has been to add a keyboard shortcut that replaces the text ill with I'll any time I add it. Not perfect, but as a stop-gap it will do.

To add the shortcut go to Settings -> General -> Keyboard and scroll to the bottom of the page. You will see an Add New Shortcut... button. Press it.

In the Shortcut configuration page type I'll in to the Phrase entry box and ill in to the Shortcut entry box and press the Save button.

Now any time you type ill it will auto-correct to I'll.