Adding a message to many posts at once

Hello everyone,

I was wondering if there is a way to add a message to many posts at once. Perhaps a plug-in or method for doing so.

Ideally I would like to be able to add a specific message to the end of all the posts of a particular category all at the same time without having to click on every single one and manually editing it.

Thanks for any help you can give,
Corey