I'm a lawyer, it is crucial to know the rules you wish to break!!!
And you should have seen the amazed looks I got with my band when I proposed to play Creep (yes, the Radiohead chestnut, I have to cater to the more youngish tastes of some of my bandmates) to be played rather than in B, D#, E and E Minor (we had to transpose it from the original G key as we have a chick singer) in G# Minor, D#, C# Minor as well as E Minor and F#! It's turned the song into a blues ballad. If you know your circle of fifths then the changes I made are kiddie stuff, but the musical transition is great, yet still retains the original harmonic environment for the lead voice. I always found the original mostly major chords kind of harsh in their progression (never mind how they were lifted off from Albert Hammond's wonderful "The Air that I breathe", I believe he knew very well he was breaking the rules when he wrote that song!).