Is it possible to modify code (obviously code that's not being run at the time) in Excel? There's a small bug in an application we recently sent out, and we want to release a workbook which, when run, will go in and modify the code.

The reasons we can't just re-release the actual workbook are:
-You can't email a 9 MB file to very many places
-Settings are stored in the workbook that shouldn't be lost
-There are technicly more than one workbooks which will be modified


To be specific, what I want is:
How do I input current code? (Locating the subroutine)
How do I modify code? (Replacing the subroutine)
Is it a different method whether I remove or add code?