The enumeration is quite clear in the French version. First, there are commas between the various elements. Second, the wording “ou dispose de son propre code” suggests that there is a choice.
However, I fully agree with my colleague's amendment if it allows for more clarity and better understanding. What I'm looking for is a clear statement that news businesses must adhere to the principles. If they do that by joining an association, so much the better. If they adhere to the principles by creating their own code of ethics, I have no problem with that. If my colleague's friendly amendment makes things clearer, I will gladly accept it.