'Factory tinting' is sometimes stained glass, which doesn't actually stop UV or heat like film tint does, hence the reason it's called 'privacy glass'. That can't be removed and would require replacing the actual glass.
Film tint is easy to remove from side windows. At my work, we use a detergent and a scraper blade.
Simply wind the window down a little so you can see the top edge, use the blade to get an edge up then (if the tint isn't too old) you should be able to rip it all off in one piece. Then spray the detergent on and use the blade to scrape off the glue (a fresh, sharp blade makes it incredibly easy).
We use a steamer to peel the tint off the rear screen, trying to get as much adhesive off with the film, then clean off any remaining glue with some detergent and super fine steel wool. You can't use a blade on them as you'll more than likely take the heater bars off the glass as well (same goes for any cargo windows with 'in-glass' radio or GPS aerials).
You seem knowledgable.
Could you tell me: When I look at the tinting certificate sticker, and it says "DOT 18", does that men 18% VLT as measured by the tinting company?