A prefab solution may exist but I haven't seen one. The logic to create it isn't undoable but it would likely require you to have well structured, consistent documents.

If you tag the main report references (eg by a Content Control or character style) and then use a specific paragraph style in the appendix, the macro could be made to run quite efficiently. I would recommend your macro then follows these steps:
1. Iterate through instances of the appendix identifier style and add a bookmark to each one.
2. While in the loop for #1, search the main report for the pointers that match your bookmarked content and replace it with a cross-reference to that bookmark.

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Andrew Lockton
Chrysalis Design, Melbourne Australia