I don't believe that setting a default driving mode and making it stick is an option in the iDrive menus. I know that it's in Bimmercode, and actually just set it successfully today on my car.
As far as coding goes, if you have a smartphone, then the Bimmercode app (paid) can do simple/common functions like this and turning off the nag screens every time you push the start button. You will also need a Bluetooth OBD-II adapter to plug into the car. Bimmercode recommends one in particular, but I'm using my trusty genuine Kiwi3 BLE adapter which is also supported.
If you want to do some of the more serious coding stuff like editing your coded vehicle order data to add an option that your car didn't come with, you will need to buy a wired "BMW ENET" cable and plug it into a Windows notebook computer with an ethernet port. You will also need to download a pirated copy of the NMW E-Sys software package, which needs the token hacks and other stuff to make it work. Not for the faint of heart.
You can also pay someone to remote code your car, or bring it to a local independent BMW shop (NOT the dealer!) to have them code it for a fee.....
2015 BMW i3 BEV, Giga World, Tech and Driving Assistant packages, 15K miles