I'm using the Excel 4 REGISTER command to add argument descriptions to my
company's suite of UDFs and function categories to the Function Wizard
(thanks in no small part to Jan Karel Pieterse). To stop duplication of
these UDFs in the "User Defined" category (and 2 entries for each under "All"
category), I can put Option Private Module at the top of each module
containing my UDFs.

This is great but these UDFs have been around for while and other people
here will have coded all sorts of calls to them. What are the ramifications
of my making these modules private? Could there be backward-compatibility
problems with other people's code suddenly falling over? I know most people
use this type of call:
x = Application.Run("addin.xla!UDF",arg1,arg2) but there could be other
types in use.