Comment: Maybe before

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In reply to comment: i don't think it gets locked (see in situ)

Maybe before

But this is what's on facebook's website now:

"You can only change the name of a Page with fewer than 200 likes"
"Changing your Page's name does not affect its username or Page address"

http://www.facebook.com/help/127563087384058/

http://i.imgur.com/N7cgu.png