It doesn't use another 10K of bandwidth.

It actually only uses a basic envelope value which is extremely low, plus only enough bandwidth to describe the delta – the change between the old post in the new post. There's no need to repost the entire content to the blockchain because it's already there. All that it needs to do is to commit a reference to the block where the original post lives and then a series of matching bits which describe the changes.

Editing is not what's eating the bandwidth on the blockchain.

If you feel like editing something, go ahead and edit it.