For e-file the original answer is correct, the software does not allow it.

For printed returns (mail in or client copy) you can print to PDF and then use a PDF Editor to add text to the top of the 1040. Or easier and stone-age; handwrite the header.

.......In biblical times text was written on a tablet. When parchment was created it was then written on a scroll. Today we scroll on our tablets. The circle of life.........