Is there any way to override a WordPress template with a plugin?

Question

I\'d like to make a landing page. If plugin detects some GET or POST requests it should override wordpress theme and show its own.

It would work somehow like that:

Answer 1

You need the hook template_include. It doesn't seem documented in the Codex, but you can find more examples here in SO or in WordPress StackExchange

Plugin file

Custom Template in Plugin folder

Result

Visiting any url of the site with ?mod=yes will render the plugin template file, e.g.: http://example.com/hello-world/?mod=yes.