I plan on testing a build in a couple weeks, but I may not have my cam pin shipment. I have other pins, but they're currently in other rifles.

Does this part "break in" to a specific carrier group, or will it tolerate being swapped out temporarily so I can test a new build?

No problem.  The only thing I'd keep with the upper is the bolt

If you are worried about it, use the cam pin AND carrier from one of your other rifles on the bolt you plan on using in that particular upper. I just don't think it is a critical decision IMHO, but it is better to err on the side of caution. Make sure & check your headspace with the B&C assembly before testing.
                                                                      HTH,
                                                                     Carey

I am using a brand new barrel and bolt from Bushmaster. I had Bushmaster check headspace before they shipped them to me.

I figured it was better to have them do it, where they can simply reach for another bolt if it doesn't fit, rather than order an unmatched bolt and have to return it if it doesn't space correctly.