Don't do it.
Don't touch the user's personal.xl* file. That's for their stuff. Not yours.
Instead, create a new workbook (or addin) and call it:
JJFUtils.xla
And share that with the users.
Tell them to put it in the same location:
C:\excelutils\jjfutils.xla
They can use Tools|addins to install your addin (or just open the file when they
need it).
By using the same location, then any UDF that you write will be found in the
same location--so the links to the file containing these functions will be found
(only useful if workbooks are shared and all recipients have that addin in the
same location).
And when you need to update something, just update your copy (with all your
protection), and blast it out to the users.
Give them the instructions to
close excel
and save the attachment (or copy from a network drive) directly over the
existing file.
========
You didn't ask, but...
For additions to the worksheet menu bar, 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)
In xl2007, those toolbars and menu modifications will show up under the addins.
And if you use xl2007:
If you want to learn about modifying the ribbon, you can start at Ron de Bruin's
site:
http://www.rondebruin.nl/ribbon.htm
http://www.rondebruin.nl/qat.htm -- For macros for all workbooks (saved as an
addin)
or
http://www.rondebruin.nl/2007addin.htm