Script Download:SetOSCEXOCalendarFolderPermission.ziphttp://gallery.technet.microsoft.com/scriptcenter/Set-Calendar-Permission-in-ad7cd4e6
Currently, Add-MailboxFolderPermission only accepts single ID as the value of Identity parameter. It requires user to provide a full folder path, for example, "userid\Calendar\Calendar 01". It's inconvenient if you want to set permission on two or more calendar folders.
You can find more All-In-One Script Framework script samples at http://aka.ms/onescriptingallery