Can a cashmere sweater be partially shrunk?

Here's what i found.

1. Get a spray bottle, fill it with the hottest water from your tap
2. Lay your sweater on a blocking board, and since you likely don't have that I guess a wide ironing board will do. Hanging your sweater on a wide clothes hanger will produce most inconsistent and uncontrollable results but it can work
3. Spray your sweater in the areas you want to shrink in. I sprayed mine all over for two sweaters, and another sweater I just targeted the arms because they were too long
4. Once your sweater is soaked with warm water, rest it on the ironing board and push it into the general shape you want. Use pins to make sure the sweater doesn't shrink more than your goal, and if you don't have pins just check it every 1-2 hours with a measuring tape to make sure it doesn't over shrink. If it shrinks to the correct dimension but is still wet, just keep an eye on it and stretch it out with your fingers as it dries into shape.
5. Since you only used a spray bottle, chances are you didn't saturate the sweater and it only shrunk a small amount. After your sweater dries, repeat the same process until you're happy

• Do not place your sweater in a dryer. You can try a delicates/garment bag and use the dryer on a low heat cycle, but there's still a huge chance for over shrinkage. It will also rough up the texture a small bit as well. If you just soak the sweater in warm water and let it air dry, you don't have to worry about fabric damage.
• Instead of using a spray bottle, you can just soak your sweater in a sink full of very hot water. You can get rid of most excess water by rolling the sweater in a large towel and evenly pressing inward (don't ever wring the sweater, that hurts the fabric). After excess water is squeezed out, you can proceed with step 4 above. This will get your sweater more saturated than a spray bottle, so expect longer drying time and more shrinkage.
• The hotter the water, the more the shrinkage
• The longer the wool strands, the more the shrinkage (merino is going to shrink quite a bit, as you've noticed)

Don't have a spray bottle? Use your clothes iron and turn the steam way up. This is a small amount of extremely hot water and it will easily replace a spray bottle. It uses hotter water than possible with a spray bottle to quicken the shrinking, but it uses much less water so it will take longer to soak to your desired saturation. I used this for one of my sweaters, I'm sticking with it over the spray.

When you shrink the sweater, the itches shrink closer together changing the nap, or the texture. I have successfully just altered one that is too large. I can do them myself, but you might want to go to a tailor to get the fit you want.