Is your enhancement related to a problem? Please describe.
We have a handful of blocks that store data in the json inside the block comment. For example, we might have something like this in the json:

{"leadershipGroup":1320}

Where leadershipGroup is the id of a term, and we need to filter the block display on the frontend (this block is rendered in php) to only show items from this particular term.

Describe the solution you'd like
Would love to have a filter as blocks are syndicated that allows modification to the json for each block in the content.. In this example, we could update the term ID to reference the proper term on the site we are distributing to.

We run into similar issues with stored media IDs, or really anything that references data specific to the original site in the block data.