What's tricky about it?? When this idea is used in music, the harmony and the melody are two separate ideas that play opposite but share some common idea, like counterpoint. As long as the melody progresses like it normally would. Meaning it can stand alone, have a singing tune, and be musical. The harmony is only a contrast and has little effect on the melody. When it does, it's not hard to quickly resolve the unwanted dissonance by moving up a step (b3-3, b5-5, or b7-7) or better remedy the harmony. Like I said it does take a lot of practice and some theory, but it's not difficult.
Often when this idea is used, the harmony is somewhat altered. In a major key the IIIm is usually bIII, and the VIm is sometimes bVI. Most rock music uses these chords anyways. Same with the VII chord which is altered as bVII. I don't know what's wrong with the IIm chord?? These are very common in rock music but in the end they don't alter the key, it's still major.
Why inappropriate? If it can be done, it's not inappropriate. The theme of November rain would support such a move, it is a sad song (that rocks BTW). Hearing someone do so and succeed competently would be very interesting. Like several great artists (michangelo, van gough, monet) all painting the same picture in their own style. This would ultimately be personal choice.
To add to chris’s suggestion on the use of this idea. Any musician new to the idea should first be comfortable with playing scales to the same key before ever trying to play against it. Generally the task should be taken to those that are looking to expand and try different things, rather than those just picking up the guitar. Better results are achieved by either writing the melody first, or with just a bass line. Since a bass line can suggest several different chords, it is easier then to find what chords should be used. Those familiar with part writing will understand.
"My whole life is a dark room...ONE BIG DARK ROOM" - a.f.i.