High voltage battery replacement - Would this really cause a problem?

From what I understand voltage is not hugely meaningful, but gives you some idea of balance. To determine the health of the modules you really need to test the capacity and performance under load of each. I believe some people have done this using a cycling charger designed for RC hobbyists along the lines of this:
Sky RC Ultimate400 Li-ion/Fe/Polymer 1-6 cells NiCd/NiMH battery 1-18 cells Charger w/LCD Display

Better still is one that you can connect to a computer and track through its cycles, like maybe this:
ProTek R/C iCharger 106B+ Lilo/LiPo/Life/NiMH/NiCD DC Charger [106b+] - $104.99 : CKRC Crawlers, RC Rock Crawlers
or preferably this, that can be extended to more realistic power levels, but starts getting pricey to do so:
West Mountain Radio - Computerized Battery Analyzer

My guess is what the reconditioners do is buy a bunch of packs, disassemble and clean up all the modules, run all the modules through a capacity/resistance test and bin them by capacity (tossing those with very low capacity or very high resistance) and then build packs out of a batch of similar capacity modules. When reassembling the pack you also have to find a way to balance all the cells. Using a charger with a repeatable cycle like that above should get you in the neighborhood, but not perfect. What I've heard of people doing to balance w/o a bms is simply tying all the modules in parallel and letting them sit for a while. In this way charge will flow from the higher voltage batteries to the lower voltage batteries, eventually getting them all even. Of course you'd only want to do this if they were pretty close to start with, as there would be no control of how much current could be delivered from one battery to another if the voltage difference was large.

Please understand I am not an expert on battery reconditioning, and have never done one. I've just read enough over the years to be dangerous

Rob