I had a bunch of lights which I made unrenderable for preview renders, then I attached them to an object, now I can’t figure out how to turn them back on. I can see the wireframes, and change the renderability of the parent object but the lights seem to be permanently unrenderable now. Is there another way to change that or do I just have to unparent them (and how do I do that?).

To unparent objects go to the Object panel
in “Object and Links” / “Relations” you find a line with “Par:(here is the Parent object displayed)” for example “Par: Cube”
click on this and delete it with backspace.

Done that, bit annoyed I can’t change the visibility without unparenting though.
Thanks for the quick answer.

If you’re changing the visibility in the outliner, you need to click the little + sign to the left of the parent; this reveals the children (lights) and the visibility/renderability buttons as well. Is that what you’re looking for?