Add user to 'All Rooms' address list

We have a custom mailbox that we are using as a 'Room' but it is still a 'User' mailbox.  I am looking to add this mailbox to the default 'All Rooms' Address List and I am trying to leverage the ConditionalDepartment field to do so.  The current filter is set to:

((Alias -ne $null) -and (((RecipientDisplayType -eq 'ConferenceRoomMailbox') -or (RecipientDisplayType -eq 'SyncedConferenceRoomMailbox'))))

How can I add the additional mailbox to the list?  I was thinking:

Set Address-List -Identity "All Rooms" ((Alias -ne $null) -and (((RecipientDisplayType -eq 'ConferenceRoomMailbox') -or (RecipientDisplayType -eq 'SyncedConferenceRoomMailbox') -or (ConditionalDepartment -eq 'Room'))))

Will this work?  Is there a better way?