Add an import type between safe and full (full without delete)

Problem/Motivation

Maybe i just miss an existing option then it would be a support request.
For lots of reasons (ci ...) we can have some custom blocks (of terms ...) that are never exported to structure sync, hence we my want to cherry pick what we export.
I'm looking for a way to update selected entity without using the "Full" import method that deletes any entity that are not existing in structure_sync_data.

Steps to reproduce

Scenario :
having 2 environments A and B
I export only one custom block from Environment A, export data and import it to environment B,
once it exists on both environments.

If i update the block's content on env. A and export it again, the only option to import it and update it on env. B is to import:block (Full)
But if i do it all custom blocks that are not exported in structure sync data will be deleted.

Proposed resolution

It would be nice to have an option to update existing content without deleting anything.
eg something like:
drush ib --choice=full --no-delete