Its very interesting what you say. Classical pieces are the untouchables. However I played the Moonlight sonata first passage with an A flat instead of A natural and it sounded nicer so I just kept the mistake in. I am a novice who is learning. Sometimes when you are not very good you have an open mind. Guy Chambers and Rufus Wainright got together in a documentary once and Rufus said I can write all of this complicated music but I can not write a simple pop song on the piano like you can. It was a very good documentary.I'm of two minds about covers. Yeah, sometimes you just want to make it your own, or spin it off in a new direction. Sometimes, it's actually tough to do things as faithfully as possible to the original. I've done songs in a completely different style from the artist. We talked about this in another thread about covers that were better than the original. Interpreting a work can sometimes be a positive thing.
I always wonder how people would feel if they went to hear an orchestra and featured pianist playing Chopin's Piano Concerto #1, and during the second movement, the piano player just took off on a tangent and winged it to make it "their own". I bet the concert reviewers would be aghast! SACRILEGE!