Hi
Thanks for your request. I think, you can use MergeField event handler to achieve this. Please follow the link to learn more:
http://www.aspose.com/documentation/file-format-components/aspose.words-for-.net-and-java/aspose.words.reporting.mergefieldeventhandler.html
Hope this helps.
Best regards,
Alexey Noskov
Developer/Technical Support
Aspose Auckland Team