A client recently asked me if it was possible to change their default Skype Audio Conferencing phone number, because the one they had been assigned was in a different city than where their headquarters was. While it is possible to do a bulk change in the graphical user interface, doing it in PowerShell was better because we could target the change to only users using the old number. Here is the one-liner powershell syntax that we used:

get-CsOnlineDialInConferencingUser | Where-Object {$_.servicenumber -eq (old number)} | %{Set-CsOnlineDialInConferencingUser -identity $_.sipaddress.substring(4) -ServiceNumber (new number)} 

To change it for an individual user:

individual user: Set-CsOnlineDialInConferencingUser -Identity (username) -ServiceNumber (new phone number)

Notes: Does not require meeting update service to run! old invites still work fine!