This actually already has a pull in place:
Currently, there's no way to add a role to the embargo administrators and ensure that it propagates to new objects. There's no way to update old embargoed items when adding new roles either.
The purpose of this is to establish a subset of embargo administrator roles that automatically get added to embargoed items, and to allow for a way (drush and interface) to update currently-embargoed items with this functionality.
There's a fairly solid test case on the pull request.
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