You could modify the code to add this in yourself, I did something similar. Here's how:
1. Add a function, e.g. "qa_content_format" to qa-util-string.php to format the string. In your case you might have something like:
function qa_content_format($string)
{
$search = array( 'shit', 'fuck' );
$replace = array( 's***', 'f***' );
return str_replace( $search, $replace, $string );
}
2. In qa-app-post-create.php call that function from the first line of the functions 'qa_question_create', 'qa_answer_create' and 'qa_comment_create' for the title and/or content, e.g.
$title = qa_content_format($title);
$content = qa_content_format($content);
3. Do the same in qa-app-post-update.php for the functions 'qa_question_set_text', 'qa_answer_set_text', 'qa_comment_set_text'.