It doesn't matter. The only items that can change on a BC upon an adoption are the parents' names and the child's name, none of which is relevant to a candidate's eligibility for office. The only items that matter are place of birth and date of birth, and those don't change.
And you know this how? Just because that's the way it may work in your state (or most other states) does not necessarily mean that is how it will work in Hawaii. They have STRANGE birth certificate laws. Ship born children can Claim birth in Hawaii.
Your point is beside the point anyway. If Obama has a "born at home" affidavit as his original record, followed by an adoption (By Lolo Soetoro OR his Grandparents) it will create a fake replacement birth certificate that looks exactly like what we see. Do you have some piece of evidence that proves this didn't happen? The circumstantial evidence implies this is a very credible scenario.