When working with fields in Word you have two different parts to consider working with: either the field code or the field result. You can change either of these via VBA but the contents of the result will be replaced whenever the field is refreshed.

When you import the this into InDesign I expect you only get the field result and it will no longer be a field in InDesign.

Are you trying to replace the characters in the code or the result? Does the import to InDesign go smoother if the field is replaced by static text prior to import?

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Andrew Lockton
Chrysalis Design, Melbourne Australia