It is a choice in the default screen listings.On the drop down bar right next to ‘Help’ the arrow button opens a vertical menu of screen options that are preset in the default. You can customise your screen set ups here. Anyway, select the SR:Text, and you will see a 3d window, a Text screen, and a button window. You can click on the lower left icon to change the text window into a scripts window.
From there, try to follow the steps I already gave you. They should work to get you the ability to save your themes in your default. Remember that saving to default saves everything, so you will need to do this without changing all the default tools and model,etc. If you need to start over from scratch, then you can find the B.blend file and delete it to force Blender to make another default file.
Try the search function, and I think you will find several posts on this subject.
Good luck, and enjoy the themes!!