I haven't needed to use the duplicate manager in a while. Maybe late version 3.2 or early 3.3.
When I've previously used the asx replacement option, the replaced files tags were all tranfered over to the created asx.
If you compared the old (now replaced) duplicate file with the asx file via the tag editor, the only thing that was different was the asx file now has the origin: field filled in.
Using it today, the majority of the tags are kept but Album, Year, Track#, Track Count & Grouping come from the 'keep file'