I tested this on the Wynaut egg, by saving before claiming it, claiming it, flying to the frontier, and performing the glitch. It did not work; I kept the egg in my team, but upon return to Lavaridge the old lady was certain she had already egged me.
Does anybody know what the partial save does and does not affect? I managed to confirm it saves your pokedex, by withdrawing a pokemon (Horsea), evolving it into a stage that I hadn't registered yet, then re-depositing it in the gap between the real and partial save, to have the Seadra still registered after powering up again.
Would there be any other way to manipulate the game to let me get multiple Johto starters from Birch? I'm on cartridge and have all gift Pokemon claimed, which leaves me no room to test methods for myself (unless I procure an emerald save file in a very specific state on PC, and even then I've run dry on ideas of where to start)
I know I can just get the other two by scrambling the DNA of poor old Dots, but I'm curious about doing it this way.
EDIT: It's come to my attention that the partial save does in fact save literally everything except the PC boxes. How hard would it be to ACE to reset the birch flag after taking a Johto starter?