Although I'm a sweater knitter, I've never knit an Icelandic yoke sweater . From what I've seen in patterns, though, all yoke increases/decreases are done above or below rounds of pattern elements.
Multiple incs/decs are done on only three or four rounds, I believe, in the entire yoke. If the sweater were top-down, you'd work the rounds of the first pattern, then several (or maybe just one?) rounds in just one color (you would have your multiple increases spaced evenly on just one of these one-color rounds), then the rounds of the second pattern, then more one-color rounds with multiple increases in one of them, and so on.
Rats! I'm not explaining this very well! Someone with experience jump in here and help me!