It is possible and I have done it successfully countless times. First you need to check if your decoder has "Software Transfer" option or something similar and a serial port. Then you need a "null modem" cable, I don't know where you can buy one but I made mine from two old serial port module connectors. Pin number 2,3,7, 8 are straight through and pin number 4 and 6 are crossed (Google for reference).
Connect the two decoders together using the cable, switch them ON and use the good decoder to "transfer software" to the bad decoder.
Obviously, the good decoder must also be connected to your TV so you can see what you are doing!