I don't know if practicing your "modding" would be the right way to say it. I think engaging yourself in the intermediate techniques of electrical engineering would better fit.
/on topic
First off i would imagine you know what a J-tag xbox 360 is right?
Well that would be what you want to do with them if they have exploitable kernels.
Thus, you could learn to program homebrew and accomplish some sweet things with some determination.
But see, with LEDs, it's as simple as - and +. So what you may want to practice is the actual art of soldering itself, or the best possible placements for lighting you xbox up. Then maybe even develop your own prototype modchip?
What i would for sure do with the broken one, is practice reflowing the board to have more experience with future xboxs, as this is a very good way to fix RRoD. After that i would harvest as many components i can, and with a few chemical baths, extract the gold from traces and pads and such.
Your possiblities are only limited to your creativity!!
Good Luck, and have fun