After some work I realized that I need to keep everything as it is, only change from cubic to quadratic or the other way round. I went for cubic -> quadratic. The conversion doesn't has to be perfect. All tools add extra points. I found out that the simplest conversion from cubic to quadratic is to offset offcurve points to 75% of their lengths. I am using brutal way of changing it with xml parser. I see that when I cmd + c a cubic contour to quadratic or the other way around font I get the desired result, which I am not able to access via code though.

@frederik huehue, ok, so we have to live with that