I have redone lots of old photos and shoot at the same locations all the time.
Whether I replace or keep both... That depends on how different the photos are.
When I re-edit a photo, I will replace the old one.
When I re-shoot a location I usually just add because it's unlikely that it's as same as the old one to replace it. Sunset, sunrise, overcast, day, night, different seasons, different angles etc.