If you want to update a template's Style definition, simply choose the 'New documents based on this template' option when making the Style update.

If you want the changes to a template's Style definitions to propagate to an existing document based on the template, apply the 'automatically update document styles' option to that document (see under Developer|Document Template>Templates).

No macros required and you can be selective about which documents are updated.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]