Is there a way to make a persistent modification to a setting, or even parameter code, that will set the Add Gamma option as a default when selecting Corona Normal map type?
I assume you are talking about a similar feature Houdini has: ‘Save as Permanent Defaults’, and as far as I know, this is not possible in Max.
Not sure if that’s possible in Max (maybe with a script?), but you can use the Corona Converter script which has a one click “fix gamma” button. https://coronarenderer.freshdesk.com/support/solutions/articles/5000549705