MySQL: Flush Privileges of Single User
This answer applies to all versions of MySQL up to, but maybe not including 8.0.


FLUSH PRIVILEGES syncs the entire set of privileges.  No way to flush just one user's.
No way.
Run the equivalent opposite action -- REVOKE &lt;-> GRANT, etc.


A full dump of certain tables in mysql:  user, db and a few others.  This is the 'source of truth' for the current state of all the GRANTs.  Editing the tables with UPDATE (etc) SQL statements has the equivalent effect to GRANT/REVOKE/FLUSH.