get_header using header.php from old theme

I needed to switch to a different template at certain pages but when I use this piece of code

add_filter('home_template', 'myfunction');

myfunction(){
   //testing on windows
   return 'C:\var\www\wordpress\wp-content\themes\DLMobile\index.php';
}

it uses the correct template file but get_header() still gets the header.php from the original theme.

My question is: is there a way to override the existing theme without actually using switch_theme? I tried using add_filter on the ‘theme’ hook but it’s still getting the same header.

thanks