My advice would be to proceed cautiously.
As Rich said, "Your fish have gotten used to the higher levels and a quick change could adversely effect them. "
Firstly, the answers to a few questions would help us give you the best possible advice.
What kind of test are you using - paper strips or liquid? You should retest again - sometimes testing right after a water change causes weird readings because stuff gets kicked up.
Can you have the test repeated by your lfs? This confirm whether or not your initial reading was accurate.
What kind of filter do you have and when was the last time you cleaned it?
When you do a water change, do you vacuum the gravel every time? Plecos are poop factories, and poop=nitrate.
What is the nitrate level in your tapwater? Leave a sample out for a few hours and test it. You may have high nitrates in your tap, especially if you use well water or live in a heavy agricultural area.
If you do indeed have 200 ppm nitrate, you would want to eliminate the cause (insufficient filtration, dirty filter, dirty gravel, high nitrates in tapwater, etc)
Then, you would want to do small water changes so as to avoid shocking the fish.
Throwing in a cheap, low light, fast growing plant would help absorb excess nitrates naturally. Java moss would probably do great in your tank - you'd be scooping out and tossing a handful every week. Beware, adding any more light to a tank high in nitrates will cause an algae bloom. That's why I'd suggest Java moss to start since it will grow in nearly any lighting condition.