Yup, they're done with it, all right. "It" being all the food being cooled for sale this week. Done.
They do not need engineers at every location to turn every knob. They need to define procedures and limits, and the ability to call the engineers when things go out of those limits. Even putting only remote MONITORING online, but requiring the local person to check and turn the knobs/press the buttons. That also adds an extra set of real eyes on the situation — when the engineer calls the local dept manager to start the defrost because the hacked line says it is now time to defrost, the local manager —with eyes on the freezer— can tell him "NO!" because this was not on their schedule and the freezers are all stocked, not emptied for the defrost.
Instead, the defrost cycle just turned on in the middle of the night, and neither the now-remote engineers nor the local managers knew until it was too late. ——Again.
Security is always a trade-off against convenience. And the idiot human managers almost always all pick convenience because their managers incentivize profit, and security costs and convenience appears to save up front. They nevermind the later costs because they'll already be promoted up or job-hopped out.