I am not very familiar with the WavePro 9xx software updates, but as far as they know they just added features and never blocked anything, so I don't think there's any harm in upgrading.
I'm not saying that DMOD doesn't work, I'm just saying it didn't on the WaveRunner LT2 (which is a lower end model). It would still be worth exploring the menus, particular the waveform math.
I recommend you read through the entire thread. Particularly the posts regarding the WavePro 9xx and WaveRunner LT/LT2, because these are very similar. For the actual software I recommend the version I linked to a few posts higher, which is the easiest to use. The software can both generate (lecroy.py gen) and decode (lecroy.py validate) keys. If you decode your existing key, it should show the scope ID, flags and mask. The mask works like a bit mask (so a bitwise AND of the option number and the mask). The flags has to match the flags your find in wavepro.txt (is technically also a bit mask). So you can construct a single bit mask covering all options for that particular flag. If you pay attention, all option numbers represent a single bit. In addition to decoding the existing key, you can also get the scope ID from your first screenshot (A878C3).