I need to update a user’s permissions in MySQL without leaving the user temporarily without any privileges. I’ve identified two possible approaches:

1. Using a transaction:

   START TRANSACTION;
   
   REVOKE INSERT, UPDATE ON mydatabase.* FROM 'user1'@'localhost';
   
   GRANT SELECT, INSERT ON mydatabase.* TO 'user1'@'localhost';
   
   COMMIT;
   

2. Directly updating the mysql system tables, although the MySQL documentation advises against this: MySQL Documentation on Privilege Changes.

My questions are:

1. Could my first method (wrapping the REVOKE and GRANT statements in a transaction) result in a very short period where the user is left without any privileges between the REVOKE and GRANT?

2. Why is directly updating the MySQL system tables not recommended?

3. Which approach is better for ensuring the user never ends up without the necessary permissions, even momentarily?