I'm not sure you can change it.

But you can intercept that keystroke and do what you want.

You could add a couple of routines to your personal.xls (or any workbook that
opens when excel starts):

Option Explicit
Sub myDateFormat()
Selection.NumberFormat = "mm/dd/yyyy"
End Sub
Sub auto_close()
Application.OnKey "^#"
End Sub
Sub auto_open()
Application.OnKey "^#", "myDateFormat"
End Sub


If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm

Loris wrote:

In Excel 2003, when I try formatting a number as a date using the CTRL-SHFT-#
shortcut, it displays as dd-mmm-yy, e.g., 10-Oct-06. I thought it might be
controled by the short date format in Regional settiongs in Control Panel,
but that shows as mm/dd/yyyy. Does anyone have any idea what is controling
the format used by CTRL-SHFT-# and where I can go to change it?

--

Dave Peterson