Adding M412 to a Production ME4024

Just wondering if anyone has added an additional tray to a production ME4024 array while online?

We have a production ME4024 which we had installed with 2 trays of expansion disks M424 and M412.

We need to add an additional M412 for expansion, but just noticed in the manual:
----------------------
NOTE To add expansion enclosures to an existing storage system, power down the controller enclosure before connecting the expansion enclosures.
----------------------
Is this still a requirement? Does the entire storage array need to be powered off to add an additional tray?