Thanks guys. I ended up changing the header space to 0.45" instead of 0.49" and then went manually through a section by section comparison against the older document to ensure the page content was the same, which demanded a number of line spacing and subtle blank-space font size changes as the header change could not be offset by any other margin-dimension modifications (there are no footers in the document).

The reason I had to do this is because two indices were generated on the older document assuming the header was fine - one index generated through the use of a Word add-in that required, since it is finicky, hundreds of references to be manually checked for accuracy. If page content changed we would have had to have gone through the process of checking each returned index reference again.

In any event, the header space modification and subsequent page-content corrections only took 3.5 hours. :-)