Yes you can use a tinted varnish to hide the yellowing without starting over. You should test it in an inconspicuous place to see how it's going to look before doing the entire floor. Just make sure that you wipe the floor with a tack cloth after the first coat dries. Sand the floor lightly with extra fine sandpaper, then rub lightly with the #0000 steel wool. Apply the next coat of varnish. Repeat the sandpaper and steel wool steps in the process before applying additional coats.
