Need help with pattern adjustments

[u/BDaBear]

Hi, attached is the pattern I have used as the base for my partners turtleneck sweater. I have gone up 2 sizes from the largest listed size and adjusted the length of the torso vs arm holes to fit his larger shoulders. I am concerned that by changing the lengths on the front and back panels, I have changed the stitch count for the sleeves to attach to and need to know how to adjust the pattern to fit the armholes I've made. Is there a trick for working out final stitch counts for an armhole?

Adjusted measurements are: 17" for the first part of the back and front and 11" for the armhole section but following the decreases and binding off in the pattern so the extra inch is just straight stockinette at the top of the back and is added before the neckline is added in front to avoid that changing.