Does a 4 wire plug for a dryer can be replaced with a 3 wire plug?

The fourth prong is a ground for the body of the dryer. The dryer will work fine with the 3 main ones. Building code requires the four wire plug now, but you can change it and the dryer will work. If you have a 4 plug outlet and a 3 wire cord, you can just change the cord and not use the second ground or connect to the the frame of the dryer.