Comment 1 for bug 2016345

This ought to be possible from the charm action itself. The architecture of the image is taken from the 'source-image' that is 'retrofitted'. From the actions.yaml for the charm:

retrofit-image:
  description: |
    Trigger image retrofitting process
  params:
    source-image:
      type: string
      default: ''
      description: |
        Optionally specify ID of image in Glance to use as source for the
        retrofitting. The default is to automatically select the most
        recent Ubuntu Server or Minimal daily Cloud image.
    force:
      type: boolean
      default: False
      description: |
        Force re-retrofitting image despite presence of apparently up to
        date target image.

i.e. if an arm64 image is used as a source-image, the resultant retrofitted image should be the same architecture.

If I've misunderstood, please do comment! thanks.