When the modifier is stressed, for instance in darkroom, or smoking jacket, the modifier suggests a purpose instead of a quality. But I would suggest a slight modification of the original formula. The alternative to stressing the first word is not stressing the second word, but giving both words equal stress.
Darkroom -> A room whose purpose is to be dark; well, it's a room whose is purpose is to develop photographs, but this requires darkness
Dark room -> A room that is dark
Smoking jacket -> A jacket you wear while smoking
Smoking jacket -> A jacket that is smoking (because it's on fire)
Cooling tray -> A tray used for cooling things
Cooling tray -> a tray that is in the process of cooling (it is being cooled)
Sleeping baby -> This isn't a real thing, but if it were, it would be a baby that is used for sleeping: I can't fall asleep without my sleeping baby.
Sleeping baby -> A baby that is sleeping
Toy chest -> A chest for toys
Toy chest -> A chest that is a toy
Peach tree -> A tree that grows peaches
Peach tree -> A tree that is peach colored
Boardroom -> The room for the board of directors
Bored room -> A room that is bored/a room full of bored people
This one's a stretch
English teacher -> English (or teaching English) is the purpose of the teacher
English teacher -> a teacher who is English
There are many more examples that seem to fit together, but I can't quite figure out the pattern. Examples are green bean (a bean whose greenness is its purpose?) versus green bean (a bean that happens to be green - ex: "A lima bean is a green bean"); Superman (man whose superness is his purpose?) versus super man (a man who happens to be super).