I started animating with Krita, and I find it so much easier and faster to use than Flash. But on one scene of an animatic, I misplaced a walk cycle, which is supposed to be at the center of the canvas, but was placed too far to the right and I can't move it to the center without having to go to all 100+ frames and moving them. So being able to change the canvas size would help a lot(not really a very serious thing if there isn't a way though, I can just fix it in the finished animation)

You can resize the canvas of an animation in the same way you can resize the canvas of an image.
Menu: Image > Resize Canvas.