Been thinking about this.
There is now a button on the New System window which says "Custom System". Clicking this brings up a new window. System Name, ID, and Coordinates are editable plus have a button to randomly select.
There will be a button to add a secondary/tertiary/quaternary star and one to add orbits to each. The grid will allow for selection of planetary type and atmosphere at a minimum. I may include gravity. The rest will probably remain random based on the planetary type.