你关于应该如何构造插件的问题有点过于宽泛，但下面是标题问题的具体答案。

要在发送邮件头之前更改邮件头，请使用wp_headers 滤器

function tsg_filter_headers( $headers ) 
{
    // For debug. This will break your page but you will see which headers are sent
    // print_r( $headers );

    // It’s a good idea to leave the admin alone
    if ( !is_admin() ) {

        // Add or redefine \'Content-Location\' header
        $headers[\'Content-Location\'] = \'/my-receipts/42\';
    }

    return $headers;     
}
add_filter( \'wp_headers\', \'tsg_filter_headers\' );