The revision author is a read only property so you can't directly do it via vba. However you have some options.
1. Create two copies of the document: one accepting all your changes and one rejecting them all. Then use a compare documents to get the differences marked as revisions while the username is set to 'ACME'
2. Edit the document with a ZIP editor and then use a text editor to globally replace your name in these xml files: word\document.xml and word\comments.xml

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Andrew Lockton
Chrysalis Design, Melbourne Australia