To leave an audit trail I recommend to add something like the following to the moderated message's body:
[Title edited by moderator to better reflect content. Original title "Hi there"]
Make sure to also set it apart via formatting from the original content, this can be done either via italic font style, color, font size or all of them. To speed up the moderation I suggest your moderators add this line with an empty original title space as a macro. This way when editing a title moderators just pick this macro and enter the original title. Keep in mind that you can use HTML in macros, so you can add a macro like:
<font color="#808080" size="2"><em>[Title edited by moderator to better reflect content. Original title ""]</em></font>
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