Method, system and computer program product for modifying installation software in a data processing system. Installation software is stored on a rewritable data storage medium using a file system that allows portions of software stored on the rewritable data storage medium to be modified without modifying other portions of the software stored on the rewritable data storage medium. At least one portion of the stored installation software is modified to provide modified installation software on the rewritable data storage medium. The invention enables modifications to installation software to be selectively placed on the same data storage medium that stores the installation software.