Hello. Currently the feature you require is not there.
But it's a useful one, I will consider implementing it in the next update, thanks for the tip.
The workaround you've posted is a valid one. In the future, I think, it will be possible just to "apply" the markup to different images, if their geometry matches the atlas.
That's awesome to hear. Thank you for the response!
If you remember and it isn't much too ask, please reply to this when/if the feature makes it in :)
For now, I swapped to using the oldschool Photoshop slices because it proved a little quicker than editing the JSON, but I would much prefer to continue using and supporting Atlased instead.