If they have OneNote notebooks in their OneDrive, then they may need to close and reopen them in OneNote. If they are using OneDrive, tell them that the URL to this location has been changed. If they are using Skype for Business Online, tell them they will need to reschedule any Skype for Business Online meetings that they organized, and that they will need to tell their external contacts to update the old contact information. They'll need it to sign in to Office 365.

This change may take a while to take effect. Tell the person the following information: You'll see a big yellow warning that you're about to change the person's sign-in information. If you don't see the option, you don't have permissions to change a user's name and primary email address. IMPORTANT: You will only see this option if you're an Office 365 global admin. Select Set as Primary for the email address that you want to set as the primary email address for that person. Select the user's name, and then on the Account tab select Manage email aliases. In the admin center, go to the Users > Active users page.

Can you change skype id