Those moves, the Arial, Mariposa (Butterfly Kick), and the back handspring are coded into every model. However, in the unmodified SP game, Kyle has no way (that I know of) to execute those moves with key commands. The Reborn are supposed to be badasses, so they execute "commands" to perform those moves.
In assets0.pk3 look in the models/players/_humanoid dir. You'll find a file called animations.cfg. Open that in notepad, and take a look.
Basically, you can build a mini mod, changing out the roll for the arial, Mariposa, or anything else. I actually made my taunt a slow Mariposa, it looks really cool, as long as you're not moving when you do it... Anyway, that file lists the animation names, the frame in the models animation to use for that name, the speed, and duration of the animation.
Think of it this way.
Command: Animation to perform:
Of course, they're listed with obscure names, and only numbers for the beginning frame. Things like the roll butterfly and arial are named as such, with some modifications like BOTH_ROLL_L.
So, find BOTH_ROLL_L, and then find BOTH_ARIAL_L and take the number values from Arial, and copy them over the number values for roll. Viola, now when you roll left, Kyle will Arial instead. ;>
If that didn't make alot of sense, maybe just downloading the coolmoves mod mentioned above would satisfy that need for Ninjutsu. Of course, experimenting around with it, now that you know what was done, can make some things alot cooler. Like a superfast backstab...