Now with software defined radio it should be a simple matter to reconfigure telemetry, IF the documentation of the equipment and the protocols is readily available.
20 or 30 years ago, it was an entirely different process and many of the signals that were received went through incredibly complicated signal chains, optimized to do things that would be tremendously more straightforward in software, some of the old equipment was actually mechanical, they did things mechanically.
Thats all they had back then.