Abstract: A method for modifying data to be used by a program of a data processing system, in particular a controller for controlling an assembly. The data is stored in a first memory in the form of reference data. The memory addresses of the reference data in the first memory are stored in a reference data memory address table in the first memory so that they can be accessed by the program. According to this method, the reference data memory address table is copied to a second memory in the form of a working data memory address table to be addressed by the program, and the reference data to be modified is copied to the second memory in the form of working data to be modified. Further, the working data memory address table is modified so that the memory addresses of the working data to be modified in the second memory replace the memory addresses of the reference data to be modified in the first memory, after which the working data is modified.