I’m going to alter this pattern a bit.
My son wants his sweater to be hooded and with a zipper . I also need to adjust the number of stitches as I use plötulopi instead of létt lopi.

First alteration : cast on 120 stitches and increase 6 stitches after the rib.

Sleeve alteration : cast on 36 stitches and increase 4 stitches after the rib.
Increase 2 stitches in every 13th row after that.

Yoke pattern alteration : skip 8 rows.

Added hood and a zipper