Wordpress Shopperpress Shipping Rates customisation

I am using the Shopperpress ecommerce theme on a Wordpress site. I need to modify the shipping options to suit my needs. The options in Shopperpress are not adequate.

I need to have 3 shipping zones: within a specific country; within Europe, outside Europe. In addition to that, I need to have a rate for an individual item and then a reduced rate for additional items.

I would obviously like the ability to change my rates.

If you could solve this problem by developing a Wordpress plugin, that would be ideal.

You might want to start from scratch, but there might be another possibility:

I have been using the Wordpress eShop plugin in another context, which does exactly what I need in that respect (more so in fact), so I wonder if we can use that eShop functionality in Shopperpress. The necessary code is therefore available in the eShop plugin (see attached). How hard would it be for you to weave that into Shopperpress? May be you have an easier way to solve my problem.