This is not unprecedented. The same thing happened for a short time not too long after Kakuzu Grudge BT came out where he was suddenly 3* instead of 4* after an update. They caught it pretty fast, and I think it was fixed before most people even knew it was there in the US servers. They also had an issue where you could buy sasuke suit and sakura cloak (playboy and schoolgirl at the time) and you could get like 80 frags for the normal price of 1. I think you were only supposed to be able to do it once, but it ended up being like 100 or something. They ended up fixing it by allowing everyone to buy up to 5 cheap boxes with 80 frags of one or the other in it. I believe it was a Sakura Mission event, but I could be wrong on that.

They could put Bee as the reward ninja in the firework event. Its not too game breaking, I crushed a friend who has bee BT and is a little higher than my power, with a simple grudge BT blitz team. Killed Bee in 1 round. And I would rather see tons of non-dodging Bee teams out there than the huge number of minato dodging teams we have right now.