OK, so, I'm not looking at a ROM now (@work) and I haven't really looked into Milon Z's dullsong counter before,
but seeing as that linked post predates FF4kster by a couple of years, I imagine the byte sacrifice was only necessary because there was no program to automatically rearrange the monster data to include a reaction byte.
So if DullSong still exists as a spell (which I don't know, but a look into FF4kster's spell editor should illuminate), then all you would have to do is give MZ a reaction, then create the reaction script using one that's not currently in use. For your convenience, Grimoire LD once went through all of the AI scripts and indices in FF4kster to identify the ones that were unused and/or dummied out. Here's that info:
http://slickproductions.org/forum/index.php?topic=1893.0