Add a Group as delegate to Room or Resource mailbox.

Just add universal mail-enabled security group to delegates ... well no.

Here's the way...

Set-MailboxFolderPermission -Identity "resource_mailbox:calendar" -User "group_to_add_as_delegate" -AccessRights Editor

Set-CalendarProcessing -ResourceDelegates "group_to_add_as_delegate" -Identity "resource_mailbox"