Change username before adding user to database

I am looking for an action that would let me change a new user username before the user is created in the database, not after.

I also need this action to happen regardless of whether the user has been created from the backend by an admin, from the default WP registration form or from a BuddyPress registration form.

Researched a lot but couldn’t find one that matches the aforementioned criteria.

Thanks,
Ran