Using predefined text in new posts

I edited the core as following and it seems to work fine:

edit-form.advanced.php…

<div><textarea rows=”<?php echo $rows; ?>” cols=”40″ name=”content” tabindex=”5″ id=”content”><?php echo $content ?>
<?php
if ($content==”)
echo ‘shit’;
?>
</textarea></div>

Thanks Moshu for the starting idea!

…but this solution is going to be overwritten by any upgrade. Is there another way to make it safe for upgrades (like the coming wp2)?

This actually still works.
I just implemented it on my blog to include a snippet at the beginning of each post, as well as a signature at the bottom.

However it does add the hardcoded text/coding again when the post is edited. Easily fixed, just a pain in the you-know-what.