I usually lay out a few blocks at a time before I start sewing them, to make sure there's no unwanted repetition. It should be easy enough to switch pieces between them at that point. As long as you use a design wall or lay all the blocks out where you can see them before you sew them together, you probably don't need to worry about it too much. I find no matter how much planning I do, I still make changes after I have the blocks ready to play with. That's the fun part of making a scrappy quilt. I'm not even terribly averse to using the seam ripper at that point, if that's what it takes. I noticed that in the sample shown the quilter has placed the same fabric side-by-side in a few places, and probably assumes that will happen. It's not a flaw but a feature. That quilt is more about the flow of colors, and you have to look at it a bit to see that blocks have a pattern that is repeated.