Oh, yes, you can create a page template in the template hierarchy that will be used for only one specific post. I had completely forgotten about this, mostly because it is very rare to do this.
For example I could create a page titled Custom Form Page
The slug for this page would be something like custom-form-page
I can then create a custom template and name that file page-custom-form-page.php
WP will use this template to display the page and this is the only page that will use this template.
The same can be done for posts and even custom post types.
