I don't know of anything you can do after the fact, and if the piece is
carved oak, good luck. Yes, you can build up several mils of finish to
make the pores less deep and easier to clean, but that would probably
come at the expense of appearance.
After the final finish is applied pore filling isn't really an option
unless the seal coat is paint.
To really fill the pores, I would think you would have to strip.