I am using OpenOffice Writer version 3.4.1 and I cannot change the margin of the header to be negative, i.e. to be to the right of the text. For example:
In the screenshot above, you can see that the header margin matches the text margin. There is a "margin" setting for header in the Page / Format dialog, but this value can only be POSITIVE. So, I can make the header more indented from the right, but I cannot move the page number any farther to the right, which is what I want to do.