Location Property [Excel 2003 VBA Language Reference]
For the HPageBreak and VPageBreak objects, this property returns or sets the cell (a Range object) that defines the page-break location. Horizontal page breaks are aligned with the top edge of the location cell; vertical page breaks are aligned with the left edge of the location cell. Read/write Range.
This example moves the horizontal page-break location.
Worksheets(1).HPageBreaks(1).Location = Worksheets(1).Range("e5")