None of what you have written detracts from using an automated mailmerge. All that is required is some care in setting up a mailmerge main document containing all letter variants and a means of telling the mailmerge which variant to output - either globally or at the individual client level. This could be done via the mailmerge filters, SKIPIF fields, or flags for each record in the data source.
Technically, there isn't even any need for all the source documents to be combined - they could be linked to a single mailmerge main document via INCLUDETEXT fields.
The same link also includes the topic Split Merged Output to Separate Documents, which is more akin to what you're already trying to do. Either way, you would do better to omit the unwanted headings from the mailmerge main document rather than trying to clear them out afterwards.
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Cheers,
Paul Edstein
[Fmr MS MVP - Word]
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