The way to do any sort of experiment like what you're thinking is to have multiple tanks. You want all variables to be the same except the one thing that you are trying to see the effects of. So for instance you could set up 3 10g tanks with salinities of 1.024, 1.020 and 1.016 and the same poundage of LR in each and track your nutrient levels through the cycle. Each tank would need the same conditions, i.e. temperature, salt type, anything you add to one you add to all.
Changing the salinity over the course of the cycle in one tank won't really tell you much, because different salinities could have different effects on different parts of the cycle, and you won't be able to tell the effects apart.
You could set up a tank with different lighting at the two ends and grow several different types of corals under each type of light. You could use two different types of light with the same color bulbs (i.e. PC vs T5), or the same kind of light with two different color spectra (ie. both PCs but one with 10000K only and one with 10000K/actinics). Light would be the only thing that would be practical to vary within the same tank, really, as temp, salinity and nutrients are going to be the same throughout. You'd want to make sure to place the corals the same distance from both light sources but that would be relatively easy.
