You will be disappointed at present it is just a function returning the
formula of a cell. However as I said it is supposed to get used across many
users and convenience in installation and use is central.

Public Function FORMELN(Zelle As Range) As String
Application.Volatile True
FORMELN = Application.Text(Zelle.FormulaLocal, "")

End Function

Using .changelinks in combination with the environmental varible
ProgramFiles sounds like a possible solution. However I then run into the
problem of running the function for each new workbook opened. As all code
should be in the add-in, none in the individual files.