For afew months now I have been wanting to attempt a pokeball style shell mod on a 3DS XL that I saw on Reedit (http://www.reddit.com/r/pokemon/comments/20uvlq/fluff_my_pokeball_3ds_xl/), so when I saw a broken White 3dsxl online for $20, I knew I Had my chance, so I snapped it up, and went and bought Myself a red 3DS XL. Unlike the reedit mod I open up the console abit more and swap out the sd slot cover and ill show you how to do it without damaging your console.
DISCLAIMER: I HOLD NO RESPONSIBILITY OF DAMAGES IMPOSED FROM THIS MOD. PLEASE READ THOROUGHLY AND MAKE SURE YOU FEEL CONFIDENT ENOUGH TO PERFORM THIS MOD
Step 1 - Obtain Consoles
Like I have already mentioned, the white 3ds I got for this project was broken (Missing Hinge and Top Screens ribbon cable is cut), so don't go out and by yourself a new white 3ds, look for broken one on eBay and look to make sure there is not too much cosmetic damage on the back, since those are the parts you are going to use.
Step 2 - Disassemble Consoles
Make sure you have ample space to work with and also make sure that you don't mind voiding your warranty on your 3dsxl console.
Step 3 - Remove Battery Plate from the White 3DS XL
Start by Removing the screws from the back battery plate.
Then you are going to open up the cover from the top first, there are 3 hooks on the bottom of the plate, so the plate swings towards the bottom of the console.
Finally place the cover somewhere, since you wont need it until the end of the mod (you can also remove the plate from the red console now aswell, like I have)
Step 4 - Unscrew and Open up the White 3ds
We are going to need the SD Cover from the white console aswell. So that means we are going to have to open up the 3ds.
First Remove the consoles battery, and then remove the Rubber Caps from the top of the console, and then proceed to remove the screws from the console, there should be 7 in total.
As you can see from the image above, the back of the case is attached by 2 ribbon cables (the shoulder buttons), go ahead and remove them to make your life easier, if you have never seen these before, imagine it like an old style cartridge, it is attached in much the same way with pins holding on, so you just need to gently lift the ends of the cable (the brown squares) from the circuit board.
Step 5 - Removing the SD Cover
To get the SD Slot Cover, you will have to do 2 things. Remove the Stylus "holster" and then remove the metal plate, being held down by the holster, which is holding down the cover. Start by removing the 3 screws on the holster, the holster should just fall away.
The metal plate should just lift out at this point (there is a latch that slides into a slot on the right side of the circle, so make sure you don't bend it), and now the SD Cover can come out, it has an L shape to it, to prevent it from being pulled out of the console so just angle it as you remove it.
At this point just put the SD slot cover with the white battery cover from earlier and place the white console aside for now, since we are going to place the equivalent red pieces in it at the end.
Step 6 - Repeat Steps with the Red Console
At this point you want to follow steps 3 and 4 with the red console. Once done, slide the white SD slot cover into the red console, make sure you attack the metal plate back properly (remembering the hook that goes under the frame), and screw the stylus "holster" back into place. Reattach the 2 ribbon cables, and flip the back of the case back onto the rest of the console and screw it back together.
Screw all 7 screw back into place and put the 2 rubber feet back onto the top holes.
Replace the Battery and then the cover, remembering that there are 3 hooks that the cover latches onto from the bottom.
Then Screw the cover back on. Do the same for the white console.
Step 7 - Enjoy
If you followed all the steps, you should have successfully created your own Pokeball 3DS XL!
.... and the left overs
Once again, only perform this mod if you feel confident enough in disassembling your 3ds.