if the vehicle is already registered in Lahore under your name you need to obtain an NOC for transfer to Karachi from Lahore. At excise office in Karachi you transfer the vehicle in sindh by submitting NOC and required documentation.
NOC from Lahore will be issued only in the name of person whose name and cnic appear under the registration number.
since e-governance you can use vehicles registered under your cnic in any province across Pakistan irrespective of where you are stationed. Online tax payment has made life more convenient.