Domain Migration/Merge

I am not sure if there was an option, may of the settings became unavailable once 1P was connected to an IDP(Rippling).

1- We are rebranding and migrating from domain W to domain A, is there a way to rename users from user @ w.com to user @ a.org while keeping their access and accounts?

2-I've also seen a few users having both a.org and w.com accounts, is there a way to merge the two under a.org? 

3-When a user is offboarded they may have passwords not saved in a shared vault, I would manually login as the user to access those. Is there an admin tool/function to transfer those vault items to their manager?

Thanks!