During installation of the version of MAMP Stack from the Apple App Store, I was never given any option as to where to install MampStack.app.
Is there some way to change it with that App Store version? How?
If not, with the version directly from BitNami? How?
No, sorry. The BitNami MAMP stack from the App store does not support changing the installation path.
The one downloaded from BitNami.org prompts you for this path during the installation.