I cannot follow you. As it is now in master (and for 0.20.1), the workflow is this:
1. Press the "Write" button
2. Press the "Edit" button
3. edit the case.sif as you like and don't forget to save your changes using Crtl+S
4. press the "Run" button
This works fine. For example when I change the mesh scaling, I get the desired result mesh size. So the solver takes the edited case.sif.
The beauty is that you this way can do everything now wit Elmer. For example add a solver setting not yet supported by FreeCAD etc.
You can change the case.sif as you like, so this is already freetext input.