Auto display CMS items and have ability to choose?

I have a bunch of cities. I want to display a set of 6 images on each page automatically.

I also want to, through the editor, be able to go in and change the images on a city by city basis (95% will just display the standard image).

Is this conditional visibility? Would I make 2 collections. 1 for the auto-display images, and 1 for the manual selections?

Then in the CMS field for the city page I would add a multi-reference field and choose to display the images on a case by case basis?