The YOs are balanced on each half of the repeat by the k2tog or the s1k1psso. So if you're going to decrease and lose a YO, you'll need to eliminate the k2tog on that side or the sl1k1psso at the other side. One way to do this is to replace half the pattern stitch at the edges with stockinette stitch. Instead of
K1, YO, K3, K2 tog, K1, sl 1, K1, PSSO, K3, YO.....K1, YO, K3, K2 tog, K1, sl 1, K1, PSSO, K3, YO k1.
You would have
K1, K2 , [u]K1, sl 1, K1, PSSO, K3, YO[/U].....K1, YO, K3, K2 tog, K1, k2, k1
The 3 sts for the underarm have been decreased and the pattern repeat decreases have been replaced with stockinette. (I've added the final k1 in assuming it's the 49th stitch with 4 pattern repeats.)
When you've used up the stockinette sts in decreases, do the same kind of decrease again to convert some of the pattern repeat to stockinette.