WordPress categories “mass edit”?

If it’s the same ‘text’ you could use the Conditional Tag in_category() to determine if you should display the text. For example in a post loop:

<?php if (in_category('3') {
echo 'If the category is 3 then display this text.  Might add this code right after the_content';
?>

Just use different if statements for each category.

Probably put that in a category template, but could be in an index.php or archive.php.

The Loop has examples.

Related:
Stepping Into Template Tags
Stepping Into Templates
Template Hierarchy