I investigated different ways to version a REST API. Most of the sources I found, pretty much all said the same thing. To version any resource on the internet, you should not change the URL. The web isn't versioned, and changing the URL would tell a client there is more than 1 resource. But actually there aren't multiple resources, it's just a different representation of the same resource. Of course there are cases where you should change the URL; for example if you are changing the API in such a way that its functionality alters. In this particular case you could consider changing the URL as you could reason that it is not the same resource anymore.
But another thing, and probably even more important, you should always try to make sure your changes are backwards compatible. That would mean there is a lot of thinking involved before the actual API is built, but it can also save you from a big, very big headache.