Hmm,
In the old days ( Mac OS 9) early (Mac OS 10) I think you could have used the update command. But it works differently now.
I am doing this on ML which I just realised you do not need to relaunch the finder for the changes to take place. You just need to make the window redraw. Like if you have a finder window in list view and make the change to show hidden files.
You can toggle a sub folders disclosure triangle and you will see the change.
The only way I can think of doing it without relaunching the whole of finder and on all windows is to flip the view to a different one and back again.
tell application "Finder"
set theWindows to every window
repeat with i from 1 to number of items in theWindows
set this_item to item i of theWindows
set theView to current view of this_item
if theView is list view then
set current view of this_item to icon view
else
set current view of this_item to list view
end if
set current view of this_item to theView
end repeat
end tell
In my tests this works so well for me I will use it to replace my current toggle script which uses the killall finder