It's really hard to say without being personally involved. Two years is a very comfortable amount of time to implement that specific change. The biggest hurdle is passing regulatory testing early enough to begin manufacturing in time to build a large enough stockpile before release. If they really pushed it and threw enough people at it, manufacturing could begin as little as 6 months after starting. But that's a very risky timeline because about a million things will still go wrong all throughout the process, and "simple" design changes like this are never, ever simple.

I'm impressed if they began production one year after deciding to make the change. The EU directive might've been approved roughly a year ago, but Apple might've seen writing on the wall and started earlier too. Regardless of context, this is definitely not a >2-3 year process though.