Force stock qty to 1 with no backorders

functions.php

<?php 

add_action( 'wcv_save_product_meta', 'wcv_custom_stock_opts' ); 

function wcv_custom_stock_opts( $post_id ) { 
	update_post_meta( $post_id, '_manage_stock', 'yes' );
	update_post_meta( $post_id, '_backorders', 'no' );
	wc_update_product_stock( $post_id, wc_stock_amount( 1 ) );
}

?>