I want to redefine it to an alternative file saved somewhere else,
Use one of Word's Builtin Dialogs: wdDialogFileFind or wdDialogFileOpen.

The algorithm is something like:
FileName = = "MyUsualFolder/FileName"

Choose = MsgBox "Press Enter to use Standard File"
If Choose = yes then Show Dialog

IF Dialog returns = Any File Name then FileName = Dialog Return
Show Dialog