To change all the headers in the workbook, select all the sheets
(right-click on a sheet tab, choose Select All Sheets)
Add the logo to the header
Ungroup the sheets (right-click on a sheet tab, choose Ungroup sheets)
You can create a new default template, with your preferred settings:
Open a new workbook.
Group the sheets, add the logo to the header, ungroup the sheets
Choose Save As
From the Save As Type dropdown, choose Template (*.xlt)
Name the File "Book.xlt"
Save it in the XLStart folder
(usually in Program Files/Microsoft Office/Office)
When you click the New button on the toolbar, the new workbook will be
based on this template.
If you want new sheets to be inserted with the same settings, you can
create a sheet template.
Follow the steps for creating a workbook template, but:
-- create a workbook with only one sheet
-- save as Sheet.xlt