IMAP filter

I just got this tip of the day from kmail:

Did you know...
...that you can get rid of the "[mailing list name]" added to the subject of 
some mailing lists by using the rewrite header filter action? Just use 

rewrite header "Subject"
   replace "\s*\[mailing list name\]\s*"
   with ""

Does this rewirite the header on the IMAP server or just locally?

I actually want to *add* the list name for some other mail clients (like my 
Blackberry).