Interior natural timber is a bit like antique furniture,it patinates with age, antique enthusiasts are reluctant to return it to a new finish.
I`ve always understood shellac (derived from insect shells, aka french polish) is a "living" finish which permits the entry of polishes to the wood, there are specific polishes for rejuvenating french polish. Lacquers or varnishes become a finish on top which seals the wood so that anything applied on top is largely cosmetic.
A "too shiny/bright" interior varnish or lacquer can be mellowed by applying a good furniture wax,using furniture grade "steel wool".It can also be used to clean and wax an old dirty finish.
I recently had success applying teak stain to an area damaged and whitened by spray near the helm station. I diluted the stain with mineral turpentine and applied coats until I felt I had it right before re-varnishing. You can tell what the wood will look like when varnished by dabbing it with a wet finger. BruceK