Dealing with external data updates for slimming down s3 buckets

[horsto]

I have a computed table that stores tif stacks as attach@my_store objects in a storage bucket.
The size of these are getting out of hand (and their costs).

I want to reduce the size of my external store (my_store) by

• temporarily downloading all of those "massive" objects
• compressing those objects locally
• re-uploading, or "re-attaching" them to the original records in place (I don't want to deal with deleting, re-inserting downstream records)

How do I handle this safely, or more specifically my question is:
What happens when I do an update1() on each record in that table that has those attach@my_store objects. Does the blob in external storage get overwritten, does it end up under a different name in external storage, how can I safely clean those old, massive blobs (my original goal) from the bucket?

[horsto]

I am aware that my plan violates data integrity principles of downstream records / calculated results, but I am willing to live with that since I suspect the divergences to be minimal after compression and I can, at a later time point, start to recalculate downstream results.