Duplicating the drawing is for altering the artwork without affecting the drawing you’ve already done. Eg. if you have drawn a hand and want to redraw the fingers slightly different, you would duplicate the drawing so you now have two different hand drawings, and altering one wouldn’t affect the other.
To make transformations (resize, rotate, change x or y pos) without affecting previous frames, you need to first lay down a keyframe on the layer at the very start of the timeline, or on the frame you would like to ‘lock in time’. Any changes made after this point should automatically lay down a keyframe.
Also, make sure you have the animate button selected (little yellow person button). If there is a red bounding box around your artwork you haven’t got the animate button selected and the changes will affect all layers/artwork.