Here's another revival of a past video that contains some valuable information about adjusting for shoulder width on a garment with sleeves.
The method I share in this video requires no change to the sleeve but be sure to watch the whole video because I have a short segment on how this alteration can change the garment's shoulder slope fit which may be problematic if you are making a very large shoulder width adjustment [1" (2.5 cm) or more].
Large shoulder width adjustments are best done using an alternate method which include an alteration to the sleeve (a future video perhaps).
The book I am referencing in the video is Fabulous Fit: Speed Fitting and Alterations by Elizabeth Liechty and Judith Rasband.
If you're interested in how to adjust the shoulder width on a garment with straps, you'll find a helpful video HERE.
All My Best,