Tweaking Motion Tracking in Motion

I have a graphic motion tracked over some video footage. However, I would like to add some hand-done keyframes before the motion tracking begins. Whenever I add a keyframe and modify the position or scale of the object, it "ripples" those changes across all of the keyframes of the motion track.

How can I lock the keyframes generated by the motion tracking while modifying what the object does before the computer generated motion tracking begins?