My grandson is long and thin. The cardigan I made for him last Christmas turned out wide and short waisted. What to do. I borrowed it back and lengthened it 3".
Close up of extension
I picked out the cast on edge, put the live stitches on the needle and knit down. Then I picked up stitches along the front edge and knit the button band. I sewed the bottom edge of the existing button band to the button band extension. The added length made it a five button sweater instead of four, but I had a set of yellow buttons in my collection. I know where the addition starts, but at least it doesn't jump out at you.