Spot-repair old varnished cabinets with polyurethane?
I want to refurbish kitchen cabinets built in 1953. They are solid, and have historical value, but are getting worn around the door handles and edges. There is a possibility that there's lead in the varnish (this was pre-1970s), so we don't want to strip the finish. We want to touch up the worn spots and edges, trying to get a color match, and then put a new coat of polyurethane over the entire cabinet surfaces (most of the cabinet surfaces are still in good shape, if a bit dull here and there.)
Can this be done safely, and what are the best techniques to use?