Stack and Reach: Why It's Your Best Friends

If you found a frame/stem combo that gave you 30mm more stack yet 30mm more reach than what you currently have, would these two theoretically cancel eachother out?

If you put enough spacers on to get exactly 30mm more stack and lengthened the stem enough to get 30mm more reach, would the two cancel eachother out?

It sounds like you’d need inverse spacers and a 30mm shorter stem.