Main part + icons part: how to override icons in main part

My snapcraft.yaml has two parts: a part with an archive with a packaged (proprietary) application and part two: a zip with an icon pack. I want to overwrite the icons in usr/share/app/icons from the app part with icons from the icon pack part. At the moment I’m getting this error:

Failed to stage: Parts 'beersmith3' and 'bier-icon-pack' have the following files, but with different contents:

This is my current snapcraft.yaml:

I think I should use something like override-stage and then compare files between the two different parts and rm duplicates with something like this:

find snap/bier-icon-pack/usr/share/BeerSmith3/icons/ -exec rm -rf snap/beersmith3/usr/share/BeerSmith3/icons/{} \;

My questions: would that be possible? Especially the part about comparing the files in two different parts? Or is there a better way to achieve this?

add something like (untested):

      - -usr/share/BeerSmith3/icons

to the beersmith3 part (note the - at the front of the path) … then only icons from the beer-icon-pack should be used …