For liability issue, the car needs to be put on 'Service Mode' when working on the car.
This might be needed also to recalibrate the rear sensors installed inside the bumper.
If it is just to replace a cover bumper, and the sensors are not damaged, a non certified shop could do it,
but if there is any aluminium panels damaged, then those need to be replaced.
If the rear quarter panel needs to be replace, then the roof needs to be removed, and the air bags need to be deactivated.
Anyway, if you get rear ended, it's the other party insurance problem. Get a police report and let your insurance handle the repairs.
One issue is to get a rental car reimbursement, in general insurances cover only 30 days while it might take several months to get your car back.