I realize these codenames are probably meaningless, and shouldn't be overanalyzed, but if we're merely looking at them at face value for fun...
Train in Soundstage 24B could potentially be Ozzy Osbourne if that rumor is true, given his hit song "Crazy Train".
Balloon in Soundstage 22 brings to mind FNAF2, since balloons can be found in the pizzeria, and Balloon Boy will have a bigger presence in the film.
But as I mentioned, I wouldn't read into these that deeply...