There is a way to neaten the neckline and to create a prettier effect. On the example here the instructions say 'K4, cast off 3, k to end'.
To make my new neckline, cast off also the last of the initial K4 stitches, so that the row reads, 'K3, cast off 4 ...'
Stop at this point and slip the last stitch off the right hand needle back on to the left hand needle, you now have only the first 3 sts on your right hand needle.
Push the point of the right hand needle into the first of the cast off stitches, from the back to the front.
Continue with the pattern instructions but on the first of the decrease rows to the neck edge of the right shoulder which in this example is a wrong-side row, check that you make a p2tog through back of the loops, thus twisting the stitches to give a left-leaning chain effect when viewed from the front (or slip 1,knit 1, pass slipped stitch over if a 'right-side' row). An opposing p2tog (or k2tog) on the second shoulder will complete a neat and attractive neckline.
This method can be used when casting off for any reason in the middle of a row; for a pocket, a sleeve etc. and I use it frequently, even on items of clothing for real people!
Please send me a message from the Contact page on my website http://www.woollywoodlanders.co.uk if you have any queries.