I have absolutely zero understanding of patent law, and have only just discovered that it's illegal for me to reproduce a game called "9 Square in the Air" for personal use due to two "ornamental design" patents they were able to secure, and because of their price purchasing is out of the question as a college student. It may sound ridiculous, since I'm well aware no one is going to "come after me" over something I build for my backyard, but I'd like to obey the law.
My friend has argued that all I have to do is modify the design in some manner in order to achieve enough of a change for it to be legal. My question then stands, what is enough of a change for a patent to no longer apply?
For example, if the result is still 9 squares in the air using PVC piping, does it really matter what else I change since it will perform the same function?