Nope.
You can save in the championship and reload to that point, but you can't exit a championship, then save and get back into it.
The save/reload trick is just a way of getting different cars or differently coloured cars. Save at the beginning of the last race (with enough points to ensure a championship victory) and do, or skip out of, the last race. If you don't gte the car you want, reload the game and try again.