Sort of. There is a setting in Logic Developer PLC where you can manage downloading to a CPU with incompatible firmware. The choices are, "Prevent", "Warn", and "Allow". By default, I think it is set to "Prevent". "Warn" means it will alert you before downloading, but you can choose to go ahead and download anyway. "Allow" means you don't get the warning. It simply goes ahead with the download.
The definition of "incompatible" isn't exactly black/white. If your program doesn't use features that have been added in newer firmware releases than what you have, you may be able to download without any problems. That most likely describes your situation since your machine was originally programmed with Logicmaster. Still, if I were in your position I'd connect a battery to the original CPU module and remove it. Then install a spare module and download to it to make sure it works. If it doesn't, you can restore the original CPU. I'm not sure if the CPU331 has provision to connect a battery directly to it, so you may have to put it in a spare baseplate with a spare power supply module. There is a good sized capacitor on the CPU, so you can disconnect it from the battery for a few minutes (they used to claim up to 30 minutes) without losing the program or hardware configuration. It's also a good idea to start with fresh batteries, given the age of the system.
