Fermentation tends to be pretty forgiving. In general, here are my guidelines for additions.
Early boil: Bittering hops, maybe straight sugars like invert sugar, etc…
Late boil: Aroma/flavor hops, other additions that are a little volatile, but pretty stable. Honey, coconut, etc.
In fermentor: stuff with volatile oils that would dissipate in heat. Fruit, herbs, peppers, tinctures, wood, etc.
