Hi Simon. That filter is currently global per form; you would not be able to target specific upload fields. The $form and $entry are not available to the filter, so you would not be able to target by field.
If you think a filter for this would make a good addition to Gravity Forms, I recommend adding a note to our product roadmap. Click the blue plus in the lower left on this page to add a note for our product team:
This snippet is based on an action from Gravity Flow PDF Generator - showing how to copy the created file to a new location/filename. Your use case would likely be similar in code but leveraging the existing gform_after_submission action.