There is disclosed improved apparatus and methodology for customizing software. With respect to GUI resources such as splash-screens, a dynamic link library containing a customer's customized resources and a default link library containing the manufacturer's default resources are prepared at design time. Source code is normally not included in the customized dynamic link library. At run time, the customer resources are automatically included by operation of a resource manager algorithm and appear on the computer terminal screen unless they were not made available initially in which case the equivalent default resource is shown on the screen. If there are any bugs which are induced by the customer's specifications to be corrected, or if the customized dynamic link library is changed for some other reason, the source code does not have to be rewritten as it is not included in the dynamic link library.