Edit - I found a way to modify older posts even if there is no button. Simply submit this URL:
Code:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?board=dev;action=modify;message=XX;thread=YYYYYYYYYY
where XX is the number of your message in the thread (with the first post being number 0 of course), and YYYYYYYYYY is the thread number. As long as you own the post, you can modify it.
Nice.
I will try that and note it down.
Mowcius