Out of curiosity, why couldn't I make a printer driver that always sent the printer data with some extra yellow dots scattered around, in an arrangement that would make the tracking codes illegible?
Perhaps the yellow dot is placed slightly off from the axies of the standard grid, making it unforgeable through input data-- I'm not sure that's what they've done, but surely they have to have considered input sanitization to some degree
That's exactly how countermeasure software works. I believe it was both the EFF and CCC that developed counteractive software for this after initially discovering it (correct me if I'm wrong).
The firmware would make sure the significant yellow dot patterns would be recognisable by not printing some of those yellow dots you tell it to print. As long as the firmware has the final say on what ends up printed there is no way you can avoid those watermarks no matter how cunning your scheme is. Stalin was right when he said "It's not who votes that counts, it's who counts the votes" - this is just as applicable here: "It's not who orders the print what counts, it's who prints the order".