It is nowhere near as restrictive as your questions imply. This is my interpretation:
1. The rule is pretty clear. If you have a prefix such as "Exits:" before the list of exits, then the prefix should not change during the game.
2. You can change both object descriptions and location descriptions during the game, but they are still restricted to two words. For example, imagine that your game starts in a "Dark room" and the only thing you can see is a "closed door". When you open the door, you might get a message saying "Light streams in." and the descriptions change to "Bedroom" and "open door" respectively. And now that the room is lit, you can also see (say) a bed and a desk.
3. Anything other than room descriptions and object descriptions can be one to six words. This includes anything in print statements, barrier messages and so on. Obviously, the messages that the user sees will change during the game, so your example with the matches is not only valid, but expected behaviour.
4. Intro and end-game messages are restricted to 3 sentences, but there is no restriction on the number of words within the sentences. With a bit of creativity using commas, semi-colons, colons, en-dashes, ellipsis and clever wording, you can write some rather long sentences.
5. I'm not quite sure what you mean here, but there is certainly no restriction on how you use treasures. All that matters is when all treasures have been dropped in the treasure room, the game automatically ends.
6. The game automatically ends when you've dropped all the treasures in the treasure room. There can be no further puzzles (which upset my game plan). If you want something else to happen, you'll have to cover it in a cut-scene in your three-sentence end-game message. At least that's what I did.