Yes, manual editing should work. What is the method that you use to edit the screen file? If you edit it outside of WireframeSketcher then after saving it you need to refresh files in Project Explorer view - right click on the project and choose Refresh. Note that you can also edit the screen file directly in WireframeSketcher by right-clicking on the file and choosing Open With > Text Editor. In this case saved modifications will appear automatically in the Screen Editor.