You can change most attributes of a custom field with a filter – but not all attributes.  For example, you cannot change the title of a custom field shown on the screen without using additional filters. But, most other custom field attributes can be changed.  Below is an example of how to change the description of  a custom field (the text shown under or next to a custom field other than its name).

add_filter( 'wpas_get_custom_fields', 'wpas_change_product_desc' );

function wpas_change_product_desc( $custom_fields ) {

	if ( isset( $custom_fields['product'] ) ) {
		$custom_fields['product']['args']['title'] = 'New Product Title';        //****This will NOT work consistently***
		$custom_fields['product']['args']['desc'] = 'New Product Title Desc';    // This will work
	}

	return $custom_fields;
}