I think chemo in general kills rapidly dividing cells, which is a characteristic of cancer cells and, unfortunately, many types of regular cells as well, hence many of the side effects, like hair loss. If it is precancerous, then probably it’s not yet dividing in that way, so probably wouldn’t make much of a difference, unless you’d actually catch the moment when the switch to full fledged malignant happens.

Chemo poisons the whole body in an attempt to destroy the cancer before the treatment kills the person. Not something you would want to do precancerous I suspect. Many of the targeted treatments we now have would also not be suitable, as they can't target (or find) a cancer so small as to be deemed precancerous. But I imagine some treatments would, such as drugs targeting the cancer DNA.