Here is how it works:
Use the "always play as Yoshi"-code and hit a morph-bubble. Instead of transforming, Yoshi will remain the same. Now you can swallow Baby Mario. And you can digest him and turn him into an egg.
Grotesque.
After some time however, Yoshi will try to "transform back", and since he IS already "transformed back" this causes an error and Yoshi will die.
Probably the punishment for murdering an annoying, yet innocent baby. o.O
NOTE #2:
XX=...
00=green
01=pink
02=yellow
03=skyblue
04=purple
05=brown
06=red
07=dark blue
Other values will lead to strange results, e,g,:
08, 0A = "psycho-Yoshi"
0C, F0 = "Anti-Yoshi"
F2, F4 = "matrix-Yoshi"
FF = completely black Yoshi and Baby Mario
SPECIAL NOTE CONCERNING JOKERCOMMANDS:
Seeing that the Advance Game Port (the GBA-hackingdevice I'm using) does not appear to support jokercommands (also known as "activator codes"),
I myself am unable to confirm if the jokercommand-toggled codes work as intended.
If you don't know what jokercommands/activatorcodes are, well they let you activate/deactivate a code during the game by pressing a button.
Some codes need jokercommands or else they are either completely useless (a moonjump without a jokercommand can not be controlled) or they will crash the game.
If these jokercommand-codes do NOT work on your Action Replay Version 3, please inform me.