Abstract: Methods and associated apparatus are disclosed for customizing and testing fully assembled postage meters in a secure manner. According to the invention, meters are customized under external, i.e. non-meter resident, program control. The external program control may be used to initialize meters, produce "blank" (unconfigured) meters, and configure either blank or previously configured meters, both at the factory and in the field. The ability to reconfigure fully assembled meters permits devices which have been put into service in one country to be easily reconfigured by authorized personnel, and placed into service in another country. The invention customizes meters in a manner that is transparent to the operator, maxmimizing the security of sensitive meter data by minimizing operator handling and access to such data. The invention also facilitates the "non-destructive" testing of fully assembled meters, i.e.