Why would a pad set come with 2 New bolts when 4 are needed?

And it's not the first time. I sorted the front brakes on a Rover and a MG in the last couple of days. Two different pad manufacturers, both 2 replacement bolts only. In fact I don't think I've ever done a set of front brakes on a Rover model that has had 4 bolts

Rant over

Can you remove 1 bolt, pivot the caliper out, remove the pads and put the new ones in?

Maybe, just. But they're only 13mm headed bolts, two seconds to release. The other thing is the sliders, into which this bolts fasten, have a tendency to seize. So it makes sense to remove and grease the sliders while you are there.

You're probably right though, just swing the caliper out rather than remove it. That's the theory anyway.