Magic Replacer gives you the option to make replacing in the entry / forum /comment posts during the publishing new one or update. Replacing makes by rules which you can setup in Extension settings page. If you have an idea how I can make this add-on more useful for you – send me PM, or contact with me by email.
I hope that interface is intuitive enough, so I will hold documentations before new add-on’s site lunch.
And remember – if you have any issue or bugs, feel free to send me a note and I will help you ASAP.
*multiselect for “where” will be added in next version.