Method to Replace A Fire Backflow Preventer?

When a backflow preventer needs to be replaced, can the two isolation valves remain in place, closed, and only the center body of the backflow be inserted in-between these isolation valves?

Would this violate the listing on the assembly if it's a one-for-one replacement?

If the backflow is listed as an entire assembly, then it seems as though an additional isolation valve on the supply-side of the backflow preventer would often be needed to shut off the system just in order to replace the backflow preventer.

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