With a mailmerge main document, that is not possible.

A macro could be used in a mailmerge main document that has been converted back to an ordinary document (thus preserving the megefields), but that would also mean having to recreate, in the macro code, the merge type, any sheet/range references, filters etc. used for the merge. Plus you wouldn't be able to change any of the: workbook name; merge sheet name; or any relevant merge range names, without updating the macro as well. Otherwise the whole process would collapse. Unless the person responsible for managing all this is a competent coder, it would be well-nigh impossible to maintain. Imagine what's going to happen when users - being users - decide to get creative and have different workbook, sheet, etc. names to reflect their area's preferences and everything is in code...

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]