Is there a way to change the data from a visa download file

We are reimpementing our system and the last thing that will be brought up todate is employees., However we need to test our Iexpense system prior to everything being up. The noraml file transfer will not work form VCF4 since all the employees are not in the system. WE are trying to see if we can either do a manual entry of Credit card charges or to modify the download so ift was only card for those employees who are already added to the system.