1. An apparatus comprising: a computer program having a number of virtual types, wherein the number of virtual types have replaced a number of original code segments in the computer program and are configured to receive new values for current values from instruction strings formatted for interactions with the number of virtual types during execution of the computer program; a header file defining a number of values associated with the number of virtual types; and a number of storage devices, wherein the computer program and the header file are located on the number of storage devices, wherein the computer program, utilizing the header file, executes by a processor unit to receive an instruction string comprising a command line switch, a new value for a virtual type, and instructions to replace a current value in the virtual type with the new value while the computer program is executing, wherein a behavior of the computer program is modified by an interaction between the virtual type and the instruction string while executing the computer program.