If you only need to thin a small area or remove a few hairs to stagger a hairline, all you have to do is spray some leave-in conditioner in the knots and pluck the hairs with eyebrow tweezers. You have to keep spraying the hair because as soon as it dries a little the knots tighten back up, but as long as it is soaking wet they will slide right out.

To thin larger areas it's best to have the factory do it. Thinning shears might work in certain circumstances, but you are taking a chance.....