Hi Jesse - there are actually 2 different ways of adding control points.

Kind of the common way in MoI is to add a new point on the control polygon hull in between 2 existing points. This way will change the shape of the curve though, it will generally be the equivalent as if you had drawn the original curve including those new points you added. That's why it is kind of the normal way because it works equivalent to drawing a curve by control points.

But there is a second way of adding a control point where you can add it directly to a curve without disturbing the shape of the curve (same as InsertKnot in Rhino). This will happen if you click directly on the curve when inside of AddPt instead of on the control point hull. But by default the control point hull (the dashed lines between control points) has priority, so if you have control points showing it can be difficult to grab a point on the curve, but if you turn control points off then you will be able to grab the curve directly for this second mode.

If you add points using the second method, the shape of the curve will remain exactly the same and instead the control points themselves will slightly shift. The first way it is the reverse - the control points stay anchored down and the curve will shift shape instead.

- Michael