Yes, you can change the difficulty in 1 player mode by changing the speed. Please have a look here http://teleball.org/doc/play.html and scroll down the page a bit until you find the headline "Speed set mode"

Hi Tarbear112, sorry for taking so long to answer. No, the signal will not interfere with a radio in a car, as I am using the 2.4 GHz band and your car uses up to 99 MHz. You can play these definitly without WiFi.