Heres the thing to keep in mind about water changes. Your fish will produce ammonia. You can cut back on feeding to keep their production down, but you won't stop it entirely. Especially since you can't cut back on feeding forever. You can do it for a week or two, but eventually you'll start starving the fish. Hopefully your cycle will be kicking in enough to start picking up some of the load by then.
Water changes tend to reduce you ammonia/nitrites by the percentage of the water changed. A 10-20% reduction from 2+ is nothing to the fish really, especially considering they may produce that much in a day or two. A 50% or higher does dent that quite a bit if done regularly (every day or two).
Also keep in mind that the fish can handle the toxic levels for a given amount of time (depends on the strength of the individual fish). They can only keep up the battle for so long though, and when their defenses come down it tends to hit rather hard. That is why keeping those numbers as low as possible (you really ideally don't want to be over .25-.5ppm, but without a bio-cycle that will be very hard) is so important.