Instead of putting the code in every workbook, you may find it easier to create
a workbook that stores all your macros.

If you won't share this file with others, then call it personal.xls.  If you
share it with others, call it KayardsUtils.xls.

Store it in your XLStart folder.

Then when excel starts, this macro workbook will be opened and you'll be able to
access the macros.

By dedicating a workbook to hold the macros, you won't have millions (er, 10s)
of files that need to be updated when the routine should change.

And to give you/users a way to run that macro, I'd either use stuff added to the
worksheet menubar or a dedicated toolbar.

I really like the way John Walkenbach does it in his menumaker workbook:
http://j-walk.com/ss/excel/tips/tip53.htm

Here's how I do it when I want a toolbar:
http://www.contextures.com/xlToolbar02.html
(from Debra Dalgleish's site)