It's easier to strip the topcoat(lacquer/varnish) rather than sand it off. I'd use an N-Methyl Pyrrolidone (NMP) stripper and let it work for a day rather than use a Methylene Chloride stripper.
Before stripping, you should clean everything off with Naptha or Mineral Spirits to try and get off any silicone that might have been used (e.g., Pledge). If you skip this, you might end up with "fisheyes" when you go to refinish.
If you're lucky, the original finish carpenters just used stain in the topcoat and it'll come off when stripping. If not, then you'll either have to resort to bleaching the stain or sanding it off (still easier than needing to sand off the topcoat as well).
Personally, I can't imagine that changing the color of the woodwork throughout your house is worthwhile. If you value your time whatsoever, it's just easier to purchase new trim and doors.