Hi Saurav,
1. There are some standard Classification defined by SAP. You can not add more classifications in your SAP CRM system.
2. Once you select BP role "Sold to party" or any other role which is copied from "Sold to party" while creating the transaction. System automatically create a Customer with Classification "Customer" and if you have the correct PIDE setting with your account group then its replicate the customer from CRM to ECC. So it's a standard behavior of the system.
3. As we know, that we can have only one mapping in PIDE from CRM point of view. If you are using different account group for your export Customer then there is one around.
There is one field available on the Web Ui "Account Group". In standard, this is a hidden field. You have to enable this field. While creating the Export Customer from CRM system, ask user to use "Account group" filed. Select "Export Account group" from the drop down option.
It may work.
Please check and share the result.
Thanks & Regards,
Dinesh