How to convert the user_key for S_PARTY, S_CONTACT, S_ORG_EXT on Siebel 7.0.5

 Hi Sir,

         Currently we import the customer data from the legacy system to Siebel 7.0.5 using customer number(CIS, 14 digits) as a user key of S_PARTY, S_CONTACT, S_ORG_EXT. Now we plan to change the legacy system to the new platform. We will convert the customer number(CIS, 14 digits) to new customer number(CIF, 19 digits) on new legacy system.

           (1) Please help advice for the best practise to convert customer number(CIS, 14 digits) to new customer number(CIF, 19 digits) on Siebel.

My propose convert steps are :

1.1  Add new Contact/Company with the user key=CIF(19 digits) only the parent table S_PARTY, S_CONTACT, S_ORG_EXT. (Note. the number of records will duplicated.)