gistfile1.php

<?php
add_filter('the_content','add_my_content');
function add_my_content($content) {
    $my_custom_text = '<hr><div class="patreonpara"><p><em>PARAGRAPH TEXT</em></p><a href="LINKURL" data-patreon-widget-type="become-patron-button" class="patreonbutton"><img src="FILEURL"></a></div>';
    $my_custom_text_other = 'something else';
    if(is_single() && !is_home()) {
      if(in_category('videos')) {
        $content .= $my_custom_text_other;
      } else {
        $content .= $my_custom_text;
      }
    }
    return $content;
}