Dynamically assigning custom category templates

category_template_filter.php

<?php
// Inspired by a snippet by Justin Tadlock (http://justintadlock.com/) posted here: http://elliotjaystocks.com/blog/tutorial-multiple-singlephp-templates-in-wordpress/#comment-2383

add_filter( 'category_template', 'my_category_template' );
// I believe *_template hooks exist for just about every type of template so it's easy to apply to other templates as well

function my_category_template( $template ) {

	if( is_category( 1 ) ) // We can search for categories by ID
		$template = locate_template( array( 'template_id_A.php', 'category.php' ) );
	elseif( is_category( array( 21, 32 ) ) ) // We can search for multiple categories by ID by passing an array
		$template = locate_template( array( 'template_id_B.php', 'category.php' ) );
	elseif( is_category( 'food' ) ) // We can search for categories by their slug
		$template = locate_template( array( 'template_slug_A.php', 'category.php' ) );
	elseif( is_category( array( 'music', 'movies' ) ) ) // We can search for multiple categories by slug as well
		$template = locate_template( array( 'template_slug_A.php', 'category.php' ) );
	
	return $template;
}
?>