No, it's only possible once per save file, per event Pokemon. Keep in mind the game might attempt to give you the same event Pokemon more than once, but the distribution will fail. It is completely random what events are given to you in what order, so it might take a while to get all of the event Pokemon.
I personally have done this. I had an old save file of Black 2 that I did this exploit on right before I reset it, so I could transfer the event Pokemon forward, and then do the exploit again on a new save file. I have received all fifteen or so Pokemon twice, and one group of the Pokemon is in Ultra Moon, while the other is still in my new Black 2 save file.
I can provide pictures of two identical event Pokemon if you'd like, it might take me a day or two.