change separator Multiple Dropdown - custom field

Hi,

The crudest method would be to change the line:
return implode(', ',$results);
in the file administrator/components/com_hikashop/classes/field.php
A cleaner version would be to do a view override of the view file displaying the area where you have the custom field and add a str_replace to change the , to what you want.
For example, if it's a custom product field, you would edit the file product/show_block_custom_main.php via the menu Display>Views and you would change :
<?php echo $this->fieldsClass->show($oneExtraField,$value); ?>
to for example:
<?php echo str_replace(', ', '<br/>',$this->fieldsClass->show($oneExtraField,$value)); ?>
to have the field values separated by a br tag instead of a comma.