Any examples of "injecting" an animation into another?

My goal:

I’m building a sign (“HELLO”) that will have a constant animation (RainbowCycle type of thing), but when an external input is provided (a tweet, a button press, http request etc), and one of the letters/a section of the led strip will twinkle. I didn’t see anything in the documentation pointing me in the right direction. Any help would be great! Thanks.

Simply put: I’m trying to run one animation 99% of the time, but “inject” a small animation for a section of the strip, given external input.