Hi,
1. Using the "Price per product" option of your shipping method configuration screen, and setting a different price for your 2 products (bottle or case) will be a good solution.
2. You'll just have to do it through your
translation file
("Hikashop->System->Configuration->Languages->YourLanguageFile") by editing these lines :
NO_SHIPPING_METHOD_FOUND="No shipping method found"
ITEMS_VOLUME_TOO_BIG_FOR_SHIPPING_METHODS="The cart items combined volume is too big for all the possible shipping methods"
ITEMS_WEIGHT_TOO_BIG_FOR_SHIPPING_METHODS="The cart items combined weight is too big for all the possible shipping methods"
ORDER_TOTAL_TOO_LOW_FOR_SHIPPING_METHODS="The total of your order is too low for all the possible shipping methods"
NO_SHIPPING_TO_YOUR_ZONE="No shipping methods available for your location"