Hi Hasse,

SD7 can fully edit the shape of stringers but currently does not allow to overshoot his boundaries. This means extending the stringer 50mm below the floor is currently not possible. You will have to use a cad program to adjust the stringer.
There is a way to do it in SD7 but the cad work is faster. You can start the stair with a landing and use a very short length of 0.01.
After this, you add your flights and add 50 mm on your total height. What you can do now is change the height of the first step which is a landing. You set it on 50mm and removed the riser and set the landing on 100% transparency. This will shape your stringer with the overshoot. You can still modeling the stringer to become the shape you need.
About the step-shaping SD7 can do this. There are 2 ways of doing it. You can go to the step-view and select the step you need. Double click on it and you are in the edit mode. You can now model your step. The second way is to right click on the step so that you can select the step-shaping feature. This will launch a window that allows you to add predefined steps and also select on specific steps. I added some pictures and the stair with the shaped stringer. This feature can always be accessed with a right click on the worksheet in stair-view.

Regards
Michel