Hack to load a different theme based on URL

functions.php

<?php

add_filter( 'template', 'switch_to_new_theme' );
add_filter( 'stylesheet', 'switch_to_new_theme' );

function switch_to_new_theme( $template ) {

	$request = $GLOBALS['_SERVER']['REQUEST_URI'];
	
	if (
		strpos( $request, '/url1' ) === 0 ||
		strpos( $request, '/url2' ) === 0 ||
		strpos( $request, '/url3' ) === 0 ||
		strpos( $request, '/url4' ) === 0
	) {
		return 'name_of_new_theme';	
	}

	return $template;
}