Default mode with USB, charging + USB Tethering?
Is there anyway to make it so that my phone, when connected with a USB Data Cable to a computer automatically turns on USB Tethering?


Yes. Use automation. I successfully tested my solution using Automate v1.1.13 on CM13 (build:ZNH0EAO1QE).

You would need to make a flow and it should fairly look like this:

(Click an image to enlarge it)




Alternatively, you can use Tasker to detect the USB connection and then run this command with root access:

service call connectivity 30 i32 1