GBP strategy for adding plumbing services to a well-established HVAC business?

[LocalInquirer]

I've got a HVAC client who is adding plumbing to his business. They've got hundreds of reviews on their well-established GBP at his primary location (primary category = HVAC contractor), but he's going to open up a second shop and I'm wondering if we should make that second shop's primary category Plumber, so we don't dilute either location. What is the standard best practice for something like this where a client adds a second different service line to his business?