Hi !
To reopen the shader source code panel, just right click on the tab layout and select shader:
For the second thing, isf shader are contained in isf file, Smode isf presets are stored in standard pack read only folder.
If you need to customize an isf, first copy the isf file in your custom media directory, you will be able to modify and save it from the shader source code editor.
Hopping all of this can helps.
Best regards