just rember the golden rules with MWBC is that never take the neutral line off at all.
it happend to me few time when i was not carefull i have few 277v ballast went up smoke [and alot of french cussing with it ]
after that i got wise get ampmeter to read the amp load on netural to make sure it is safe but anytime you work on pretty large commercal area it can be pain in butt when you try turn off the lumiaires for mantaice work especally with ballast that will compound it.
i know one place they wont let me turn off the light when the ballast is burn out i told them sorry i want to turn it off when i work on it some case it take act of god to do it
Merci, Marc
