I am making very good use of StepUp these days in my current project. Thanks so much maui for providing these great utilities. As I understand from the above, what you want to do to update the PCB edge is to re-import the board into FreeCad with StepUp, and replace the sketch in that imported file with the original saved one with the constraints. However when I do that I am getting an offset in the position of the PCB edge. I am not sure I understand the last point, which could be my problem: Were in KiCad are one to set a PCB file static design reference to the preferred choice Grid Origin? Does that differ from the default setting?
[edit: to make it clear, the offset already appears in FreeCad after replacing the new sketch without constraints with the old one with the constraints].
What has worked for me without producing an offset is a manual procedure: Rename/make backup of the edited Pcbnew file. Let KiCad create a new blank pcbnew file. Import that into FreeCad and copy the sketch of the saved FreeCad file that has the board outline with the constraints to replace the original blank sketch and edit it to your liking. Save it and push the edge back to the blank PCBnew file. Edit the PCBnew file that now has the updated edge with a text editor and replace everything except the PCB edge with the information from the original renamed PCBnew file. (I found the board edge is conveniently placed at the very end of the PCBnew file so it is very easy to do these edits in a text editor).