But in reality sometimes its just best to refinish the complete stock. Matching will come close if the person is good at it, but under a direct light or sunlight one can always tell where the old finish and the new come together...
Lots of good tips, but what he said.
If I'm the one (or whatever person) is the one who finished it, you can bet a repair will be spotless as they have the same finish to use in the repair.
IF wood has been removed in the attack, best to strip, and flat sand that area out to hide after trying to swell it up. Good luck whatever route you take, but I'd say skip the attempt at repair and proceed directly to refinish.
