Keep in mind that you may lose stored funds if you switch shops back (that happens on Wii, but I haven't confirmed for 3DS). The free games thing seems to be worldwide, so I suppose you'll just get the Brazilian offerings. Then again, if there is no official announcement for Brazil, maybe they aren't dropping the price :/.
Also, given that you switched stores, it's not certain you'll qualify if you switch back after the deadline, as it may treat your US account as deleted or inactive. If you don't find anything about a Brazilian version of the offer, it might be best to spend as much of your stored funds as you can, switch account to US, and then link, get all your Club Nintendo coins and count for the offer at the same time.
Of course, any of my suppositions here could be wrong.