Until Tiger is loose and we can all use smart folders to organise emails into multiple places at once, I thought it would help me enormously to be able to merge thread conversations. I work in thread mode, but sometimes there are messages which, for whatever reason, fail to make the criteria and get left out. I wrote this script to change the subject lines; select the messages you want to merge in the list, then run the script:
tell application "Mail"
set theSubjectList to {}
set themessages to selection as list
repeat with msg in themessages
set thisSubject to (subject of msg as string)
if thisSubject is not in theSubjectList then
set theSubjectList to theSubjectList & {thisSubject}
end if
end repeat
set theNewSubject to ¬
(choose from list theSubjectList with prompt ¬
"Choose the subject of the merged thread…") as string
if theNewSubject is in theSubjectList then
repeat with msg in themessages
set subject of msg to (theNewSubject)
end repeat
else
display dialog "Action cancelled"
end if
end tell
Save this AppleScript in ~/Library -> Scripts -> Mail Scripts, and it will appear in the script menu in Mail. There are a couple of caveats, though. In order to see the reorganised threads, you have to unorganise and then organise again from the View menu. I tried it with scripting, but UIScripting doesn't work while the script menu is being used, and I couldn't get the proper commands to do it, either.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20041021072014781