How do you delete a Profile-enabled AEP Individual Profile schema?

I need to delete two XDM schemas in a development sandbox and I've hit what looks like a closed loop. Hoping someone has been here before.

What I'm trying to do

Some field paths in our dev sandbox differ from prod by character case only - for example campaignUseCase1 in dev versus CampaignUsecase1 in prod. Since XDM field paths are immutable once created, I understand the fix is to rebuild the field group and schemas correctly rather than edit them in place.

Where it breaks

I can't create the correctly-cased fields while the incorrect ones exist, because both paths would land in the same Profile union and AEP rejects paths that differ only by case. So the old objects have to go first.

But:

1. I can't delete the field group - two schemas compose it.
2. I can't delete those schemas - both are Profile (union) enabled.
3. I can't disable Profile in the UI - the toggle is there but Save stays greyed out.
4. I can't remove the union tag via API. PATCH on the schema with {"op": "remove", "path": "/meta:immutableTags"} returns:

XDM-1501-400  meta:immutableTags Missing"The schema's meta:immutableTags array could not be found. Once this field is added to a schema, it cannot be removed."

Already checked

• Confirmed both schemas carry meta:immutableTags: ["union"].
• For one of the two schemas, I deleted its only dataset — zero datasets now reference it, and the schema still won't delete.

Questions

1. Is there any supported way to remove a schema enabled for profile, or is it genuinely permanent for the life of the schema?
2. For anyone who has fixed case mismatches between sandboxes - did you go through this, or is there a cleaner approach I should be taking instead?

Sandbox is non-production, so I'm happy to lose the data. It's the schema objects themselves I need gone.

Thanks.