child theme & syndication help ( rss feeds )

i have created a working child theme, in the folder i have a .css & funtion.php file but im not sure if i need to create feed.php for this syndiction issue. With good forum support (step by step instruction) i have been able to make progess with my blog.

i want to control # of post shown from different categories ( blue category shows all 10 post but want green category to show 1 – the most recent, have been trying for days but dont know what im doing..

this is what i was try, placing code in my function.php ( fail )
remove_all_actions( ‘do_feed_rss2’ );
add_action( ‘do_feed_rss2’, ‘green_feed_rss2’, 10, 1 );

function green_feed_rss2( $for_post ) {
    $rss_template = get_template_directory() . '/feeds/feed-green-rss2.php';
    if( get_query_var( 'post_type' ) == 'green' and file_exists( $rss_template ) )
        load_template( $rss_template );
    else
        do_feed_rss2( $for_post ); // Call default function

}

im lost & needs lots of help !!!!
any help would be great ..
thank you

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