No difference between a used and new as far as coding/adaptation/CP. You don't have to match the odometer to your car. Mine was new and doesn't match because the dealer didn't match it (and I didn't catch it soon it enough
). No impact to having the miles not match, just have to be careful if you have a shop work on the car that they don't report the incorrect mileage (if your cluster has less miles than the car). The mismatch would show in CarFax report. If you don't plan to sell it's no big deal. I have a sticky note in the glovebox that says Actual mileage is odometer + xx miles (from when I had the AID installed). I stick it to the dash when I bring it in for any work, hasn't been a problem for the dealer or any shop yet.
IF you're gonna have the dealer do it they may push back
more because it's a used cluster, but it's an off-book task for them anyway so shouldn't matter.