Study Curve

Like weischris said, as long as it sound right you can be in or out line. Listen to the key and follow the pattern. Your ear is the best judge when is related to music.

i guess just stay in or out of the line

ideally, yes. Like Belle said many jazz musicians will experiment, and if you know what you are doing it can sound great. I was classically trained on piano and taught YOU CAN"T STRAY, but listen to jazz and fusion and alot of different music and you will hear it. It's going outside the box, like forming proper sentences with punctuation and all that. It works, but some people get away with risky stuff. e.e. cummings comes to mind for someone who experimented and was amazing, on the music side listen to Thelonious Monk he played with variations all the time and is now one of my favorite jazz pianists.

Yes, it is important to stay inside key signature. When composing,
especially beginners, one should work within the eight diatonic
pitches/tones and work within the given scale. More experienced composers
sometimes go outside the signature for a short time for effect. Jazz
musicians do this frequently.