You see the problem. The mainframe computers of the 1950s and 1960s and the PCs of the early 1980s have been replaced several times, but many organizations have been reluctant to abandon crucial computer programs that still work and that would cost a small fortune to replace. As the end of the century approached and the cost of computer memory and disk storage dropped to a small fraction of what it was in the early days of computerization, programmers began developing new programs that use four-digit years. The original programmers often poorly documented the programs they designed. To figure out how one works, today's programmer has to painstakingly analyze each of possibly thousands of lines of code.
Many programs interact with other programs.
Changing the way one runs could affect the way others run. Programmers today write few programs in the computer languages used in the 1950s and 1960s. As a result, few people have the skills to revise the old programs. Do it in writing and ask for a written response. Provide details about your system.