Changing the default diacritic type when pressing Option+ letter

Bren_O wrote:

I've already installed Maori in the Language and Region preferences

That's the wrong place. You need to add Maori in system preferences > keyboard > input sources.

https://support.apple.com/guide/mac-help/type-language-mac-input-sources-mchlp1406/11.0/mac/11.0

and

https://support.apple.com/guide/mac-help/use-the-keyboard-viewer-on-mac-mchlp1015/11.0/mac/11.0

There is no way to change them. I'm not sure if a keystroke modifier would be able to.

However, you use a specific Option+letter for a particular diacritical, depending on your keyboard layout. You can then type the character you want to modify.

Option+e is used for ´ ; Option+I is used for ˆ; Option+e, i produces í

With the US Extended keyboard layout, you can generate a macron with Option+a. e.g., ō. On the normal US keyboard, Option+a produces å. You may need to see if there is an Extended Maori keyboard layout.

Additionally, you should just need to hold down the letter for a few seconds and a list of options will appear.