There is a webservice that enables you to edit messages or even topics
Note that you will only be able to edit the title of a topic by editing its first message. However, if you edit the first message of a topic and then send an empty string, the "title" will not be modified.
Here are the parameters:
user : Pseudo of a forum administrator
pwd : Password of a forum administrator
idforum : ID of the forum where the message should be edited
idcat : ID of the category where the message should be edited
idtopic :ID of the topic that contains the message to be edited.
idpost : ID of the message to be edited
title : title of the topic duing tis creation
text : text of the first message of the topic
Here is a script example based on the Message Edition Webservice, done in PHP
If everything goes right, the message or the topic will be edited and will return the 2 following parameters
idpostedited : returns the ID of the edited message
status : Returns the status of the edition