Hi,
Normally, that's not how you do it. You need to create one custom field for each row of information you want to display. HikaShop will display under that specifications tab a table of your custom product fields, with the values entered / selected in each custom field.
Now, I think the Wysiwyg custom field code is missing a piece to handle default values.
Add the code:
if(strlen($value) < 1 && !empty($field->field_default)){
$value = $this->trans($field->field_default);
}
before the line:
$editorHelper->content = $value;
in the file administrator/components/com_hikashop/classes/field.php and it should allow you to get the custom field default value when editing a product.
Let us know how it goes so that we can add the patch for the next release.