It's still kinda risky with a few random bricks from people who followed the instructions and even validated their rebuilt nand with an emulator. downgrading involves dumping the nand, then modifying it on a pc with older versions of files and crossing your fingers when you flash it back hoping you didn't just brick.
if you don't have a lot of experience, i'd get a cheap flashcard for ds homebrew and wait, I've modded a lot of my systems but I've held off on modding my dsi since it's still sketchy.
check some of the popular threads for ugopwn and downgrading here to get an idea of what you'd be doing.