Anyone have any idea to customise shipping

Hi I am running cs-cart MV, and have made a couple of changes to allow the multi-vendor to show one single shipping cost instead of accumalting for each vendor.

Although this works for now it is a bit of a hack, as I am not able to add multiple shipping methods now. So my question are:

Does any one know how to make the multi-vendor deliveries/shipping work the same as the professional version?

If not does any one know how to add custom fields in the checkout that will update total price when selected?

Would really appreciate the help.