you can make it with the Variable/Conditional Events, for a simple example, make a brick anywhere on the map, that no one will expact it to do anything but support some building or something, than use this:
OnActivate -> Client -> AddVariable (admin) (1)
than for the special door or brick you want do this:
OnActivate -> IfVariable (admin) (GreaterEquels) (1)
OnVarTrue -> Self -> DoorOpen/Dissapper
OnVarFalsh -> Client -> CenterPrint -> "This is admin only"