I have not delved into the options much. Which one are you curious about?
The built in optional rules can be found by clicking on the gear icon in the upper right corner.
https://i.imgur.com/Y6D3VQn.png
I don't see one for overcasting. However, you can house rule that.
There is nothing preventing you from adding spell lists at any time, so that one is pretty easy to do, just go to the Spells tab and add the list, you can use the drop down boxes to find it (use the scroll wheel to scroll down the list).
https://i.imgur.com/HoIDTpb.png