If you're not gong to refnish the entire floor, the best way to mask a repair to a floor that has a cured finish is to sand each board that is scratched in its entirety. Meaning, if a plank needs to be refinished, sand the entire plank, full length and full width. Mask off the boards that have been sanded from their neighbors, then topcoat.
The newly topcoated areas will have a slightly different sheen, but that differential will disappear over time. You can help it along by buffing as required.