Unless you are able to specify otherwise the bike will come with a fairly long steerer - then you can cut it down to the height you require, when you get the bike set up as you like it. You can't make it longer if the stem has been cut - obviously?
totallyfixed - are you serious? Are you still riding in quill-stem land? Nowadays bikes come with aheadsets, and steerer tubes and separate stems. Look carefully at the Giant above and you can make out the spacers (4? - 2 thinner, 2 thicker) below the 2 bolts on the side of the stem. The usual advice is to keep one thin spacer (2mm) above the stem to ensure preload, and one below. The tapered spacer on the Giant would be adequate.
edit - totallyfixed missed your last post - my apologies .......