How to Override Page Template if URL matches query?

Question

I have 4 Page Templates that my theme uses for all the pages - Default Template, Template One, Template Two and Template Three.

When the relevant Page Template is selected, it loads an Advanced Custom Fields Group which enables the user to build/design a specific page - i.e. Template Two is for an F.A.Q page, Template Three is for a photo gallery.

I have added 4 new links in the Admin Sidebar which directs the user to the "Add New Page" URL - "post-new.php?post_type=page". For each link, it appends the name of the template at the end of the URL i.e. "post-new.php?post_type=page&template=three".

I would like to have the Edit Page load the correct Page Template depending on the template dictated in the URL - "template=three" would load "Template Three".

I am able to do a check with the URL and form an if statement with the below code --

list($uri, $templateURL) = explode('&', $_SERVER['REQUEST_URI']);
    if ( $templateURL == "template=services" ) {    ...

I am struggling with how to hook this into functions.php. I have tried editing the below ( https://wordpress.stackexchange.com/a/231503/182411 ) but it isn't working:

function wpse196289_default_page_template() {
  global $post;
  list($uri, $templateURL) = explode('&', $_SERVER['REQUEST_URI']);
    if ( 'page' == $post->post_type )
    && ( $templateURL == "template=services" )
    {
      $post->page_template = "page-mytemplate.php";
    }
}
add_action('add_meta_boxes', 'wpse196289_default_page_template', 1); 

Answer 1

The first issue I can see is you're missing a wrapping set of parentheses on your if statement:

your code: 

if ( 'page' == $post->post_type )
&& ( $templateURL == "template=services" )
{...

should be:

if ( 'page' == $post->post_type && $templateURL == "template=services" )
{...

I don't know for sure if that will fix your problems but it's a definite problem.

Is there a specific reason you want these to be pages and not custom post types? If you were to create three custom post types, you'd be able to use the templates as singles for your posts, which would apply your styling and ACF fields. It's a less hack-y solution as well.