I've no clue as to why this would ban your 3ds, I don't think they can detect your browser version and ban you for it, I don't think they can, but they can detect games that have been changed if you add a "weird and obvious" cheat code... but ban you just fot the browser version I think not! But I can't garantee nothing...
Does any body know if this is possible?
You should backup your firmware because you're installing a previous version of the browser over the current version, and these are system data, something can always go wrong, though unlikely, they CAN happen... like 1 in a bilion tries... maybe...
PS: AGAIN, DON'T TRIPLE/DOUBLE/MORE THAN ONE POST before someone answers your post! JUST EDIT IT!