How to replace, on a curve, a corner point by an ordinary point and vice versa?
I get there by tweaking:
1_ I create an added point with the point command, it snaps to the corner point (which is a control point!) Of the curve.
2_I hide the added point and delete the corner point (which is a control point!).
3_ I reactivate the hidden point and with the command "add pt" I add an (ordinary!) Point to the curve. But the placement is approximate because there is no possible hooking on the reactivated point which is well placed.

Zooen