No, there's nothing new here.
If you overwrite the 400.vps file, the About box will probably show the new version - but the new database will not be loaded into memory (i.e. used, even in newly started on-demand scans) until all the running scanners are killed and restarted (which includes the resident protection) - that's what I'm quite sure about. Of course, restarting the computer (after the file is overwritten) fulfills the condition.
Regarding the replacement of the updated file by avast! setup - here I am not sure, I really don't know, just saying that I can imagine such a scenario. (But certainly a reason for not recommending this method
)