Wordpress - How does one suppress a 404 status code in a WordPress page?

You can either add custom rewrites to your pages. Or on the top of the template files that wrap your other pages just output header('HTTP/1.1 200 OK');.

WordPress offers the function status_header() to return the correct status-code.

You can call this function inside your WordPress template/function:

// Will return http status header "200 OK"
status_header(200);

Wordpress is PHP, so look for where it's sending something like:

header("HTTP/1.0 404 Not Found");