I will give to you a simple trick. I will use a example for explain that. Look at this code below. I Will use Related Post Plugin’s code.

Example:

<?php related_posts(); ?>

With if and function_exists:

<?php if(function_exists('related_posts')) { related_posts(); } ?>

We use related_posts twice. But with this code the plugin don’t make any problems after deactivating. You can apply this code all plugins  which one have a short code like Related Post Plugin.

Yep, lets start!

We cnahge our core single.php also you have to make a back-up this file. And you have to make 2 copy of this core file, and single-blog.phpsingle-default.php (single-default is a copy of our core file). And upload these 2 files to your host (in template folder). After that, open your single.php on your server (with a ftp program ex: CuteFtp) and clean all code in this file and add this codes to single.php ;

<?php
$post = $wp_query->post;
if ( in_category('3') ) {
 include(TEMPLATEPATH . '/single-blog.php'); }
 else { include(TEMPLATEPATH . '/single-default.php');
}
?>

We make a duplicate with this code. But we give a special command to this code. With If, we said to code “if we click a post in category 3 you have to call single-blog.php to us“. If we get a normal category post, our core single.php call single-default.php to us. After this code our core single.php will be a tunnel page for us.

And if you wanna make more single pages for your different categories you can duplicate this code.

Here is the second code:

<?php
$post = $wp_query->post;
if ( in_category('3') ) {
include(TEMPLATEPATH . '/single-blog.php'); }
elseif ( in_category('15') ) {
include(TEMPLATEPATH . '/single-foto.php'); }
elseif ( in_category('18') ) {
include(TEMPLATEPATH . '/single-video.php'); }
else { include(TEMPLATEPATH . '/single-default.php');
}
?>

Have a nice day!