2021 update:
The following answer is outdated and replaced by the following thread instead: Set and display a custom product variation value dynamically on WooCommerce single products
This is much more complicated as it's a live event on client side, so javascript/jQuery is required and some more code:
// Set the defined product attribute taxonomy
function vendor_defined_taxonomy() {
// The targeted product attribute taxonomy
return 'pa_apple-id';
}
// Display the vendors on product meta
add_action( 'woocommerce_product_meta_end', 'display_product_vendors', 10 );
function display_product_vendors() {
$taxonomy = vendor_defined_taxonomy();
$term_ids = wp_get_post_terms( get_the_ID(), $taxonomy, array('fields' => 'ids') );
if( sizeof($term_ids) > 0 ){
$label = _n("Vendor:", "Vendors:", count($term_ids), "woocommerce");
echo get_the_term_list( get_the_ID(), $taxonomy, '<span class="posted_in vendors">' . $label . ' ', ', ', '</span>' );
}
}
// Display the selected variation vendor in a hidden imput field
add_filter( 'woocommerce_available_variation', 'selected_variation_vendor_value', 10, 3 );
function selected_variation_vendor_value( $data, $product, $variation ) {
$taxonomy = vendor_defined_taxonomy();
if( isset($data['attributes']['attribute_'.$taxonomy]) )
$term = get_term_by( 'slug', $data['attributes']['attribute_'.$taxonomy], $taxonomy );
if( isset($term) && is_a($term, 'WP_Term' ) )
$data['variation_description'] .= '<input type="hidden" name="vendor-hidden" id="vendor-hidden" value="'.$term->name.'">';
return $data;
}
// Replace the vendors on product meta by the selected variation vendor
add_action('woocommerce_after_variations_form', 'custom_product_jquery_script');
function custom_product_jquery_script() {
global $product;
$taxonomy = vendor_defined_taxonomy();
$terms_string = $product->get_attribute($taxonomy);
if( ! empty($terms_string) ) :
?>
<script type="text/javascript">
jQuery(function($) {
var form = 'form.variations_form', selected = 'input[name="variation_id"]',
vendorVal = 'input#vendor-hidden', vendorTarget = 'span.vendors',
vendorHtml = $(vendorTarget).text(), vendorLabel = '<?php _e("Vendor:", "woocommerce"); ?>';
// Once DOM is loaded
setTimeout(function() {
if($(selected).val() != ''){
$(vendorTarget).text(vendorLabel+' '+$(vendorVal).val());
}
}, 300 );
// On variation select
$(form).on( 'blur', 'select', function() {
if($(selected).val() != ''){
$(vendorTarget).text(vendorLabel+' '+$(vendorVal).val());
} else {
$(vendorTarget).text(vendorHtml);
}
});
});
</script>
<?php
endif;
}
Code goes in function.php file of the active child theme (or active theme). Tested and works.