I recently found out that you can run JavaScript on the shopping cart. (See post "Limit one per order")
I would like to use a similar solution on a different problem.
We use three methods of shipping, all through the US Post Office. They are:
International - all except USA orders MUST use this option
Media mail - cheaper, but slower, and you can't choose this option if ordering some products
1st class - for all other orders
We often have International orders choosing Media mail or 1st class, or orders for Media mail that contain products banned by the Post Office for Media mail. As it is, our store does not catch the errors and we must call the customer.
In the code for Limit one per order (see ShopSite tutorial on limiting a product to a maximum quantity: http://support.lexiconn.com/news/viewtopic.php?t=415), gives the ShopSite code for accessing the SKU number for items in the shopping cart (ss_sku).
What I am hoping for is the code to access and change the shipping options. I would also like to access the postal code the user is entering.