excalabyte

For anyone else the following needs to go in your functions

/** pastcode plugin */
add_filter( 'pastacode_langs', '_pastacode_langs' );
function _pastacode_langs( $langs ) {
	$langs['powershell'] = 'Powershell';
	return $langs;
}

add_filter( 'pastacode_tinymcevars', '_pastacode_tinymcevars' );
function _pastacode_tinymcevars( $pvars ) {
	$pvars['scripts']['powershell']=get_template_directory_uri().'/js/powershell.js';
	$array=array(
			'libs'      => array('powershell'),
			'mode'      => 'application/x-powershell',
			);

	$pvars['language_mode']['powershell']=$array;
	return $pvars;
}

add_action('wp_enqueue_scripts', 'mytheme_scripts');

function mytheme_scripts() {
  wp_dequeue_script( 'prismjs' );
  wp_deregister_script( 'prismjs' );
  wp_enqueue_script( 'prismjs',  get_template_directory_uri().'/js/prism.js', false,PASTACODE_VERSION, true );
} 

Along with prism.js and code library file (e.g. powershell.js ) in a js folder in your these