My MYMODULE_config_preprocess_node(&$variables) is not displaying my variables
I think you're halfway there! The thing is that it isn't enough just to set the variable in the preprocess function, now you have to go one step further and output it in your tlp.php template file.

So, find the correct template file in your theme that you want to use (is it a general node.tpl.php one or a one for a specific content type like node--article.tpl.php), and edit it to actually output the variable you've set.

So, in the tpl.php file you're using, you should have something like:

&lt;?php print $my_stuff; ?&gt;


Otherwise, you've set the variable, but never display it.  Does that make sense?  Is that what's going on in your case?