Do you have to do it [set the transition preset tag and offset ID] for each light?
TL;DREach light needs its transition set individually, which gives fine, powerful control but takes a lot of iteration to make the transitions feel natural for the type of light.
You do have to do it for each light. But it does mean that, like Chris was saying, you have a very fine control and it's quite powerful in terms of if you have a vision for exactly what you want to do and you know how to do it, you can get some quite interesting complex transitions. Not that I can do that right now.
It's a lot of iteration time figuring out what feels natural. It's a balance between what feels natural for how lights would behave, what type of light it is, if it's a compact fluorescent, which slowly flickers before the power comes on, something incandescent where it has to burn for a little while before it reaches its full brightness, that kind of stuff. It takes a bit of iteration to go back and forth, and you test the animation, you test the transition, you see if it feels right, you find what elements don't feel quite right, and you go and you tweak them a little bit.