Yes the remote panel button commands work, although I haven't used them myself. There was a recent video of a massive DX7 controller (not Jellinghaus or any commercial ones) that an individual made himself in the 90's (?) and he confirmed that he used those commands during development. I think his final project ended up being a DX7II or DX7S controller though. Great video for it on YouTube released over the past few months if memory serves.
In my snooping around I think I found commands for reading the LCD buffer as well, but that info will require some detective work on my behalf. Probably these were used for Yamaha engineers initially.
