remove product title woocommerce if custom field exists..

im using this here

function rep_title()
{
     echo 'stuff';
}
remove_action('woocommerce_single_product_summary', 'woocommerce_template_single_title', 1);
add_action('woocommerce_template_single_title', 'rep_title', 10);

ive tried different priorities but i cant get it to work, it either has no effect, or the title simply does not display at all…as i change the priority.

how can i do this and replace the product title with custom field value, on single product pages only?

any ideas?