Office 365, Email, Exchange, Global Address List, Remove / Hide address from the GAL

Is it possible to have XYZ removed from the global address book, but still have the account exist?

Yes, this can be done via Powershell by the service managers. Please email consult@illinois.edu with this request.

Please note this will also prevent the account from being added to Outlook.

IT Pros with access to the AD Tool can hide distribution groups themselves.