If it was me, i wouldn'd do it. It wouldn't hurt anything, but it may not really extend the life of the pipes either.
You need to get the rust out from inside (with an additional chemical) even if it is just starting to form as the used set you are getting will have rust starting already. Check around your local area, I have heard that you can sometimes get them coated for under $100. They normally should acid dip them, clean them, inspect welds (and usually repair any, included in the cost) then coat, and bake. The high end companies do both inside and out. Smaller ones may want to charge extra for this.
