Insert Code into Header Only on Blog Posts

Yes. In your functions.php file, add something like the following:

function my_post_header_function() {
   if( is_single() ) {
      // Your Code Goes Here
   }
}
add_action( 'wp_head', 'my_post_header_function' );

What this will do is execute this when wp_head() is fired. It will see if you’re on a single post (NOTE: This will not work on pages or attachments) and if you are, it will execute the code you want to put.