Question asked by you is very difficult to answer and should be answered by Structural Engineer only who can specify the tolerable limit of shifting of position of bar.
Practically the bar does get shifted during construction within column core area due to practical issues or human errors. and mostly all civil engineers does not think it as a serious issue until the bar is having cover to it and in core area.
We should make all possible efforts to keep bars in position as per the structural designers instructions and drawing.
An bar shifted from its position is normally adjusted by joggling it a ratio of 1" in 2 feet.