IMO the best way to go about it in this case would have been simply to express your appreciation/admiration/whatever for his actions here, and ignore the past. That would clearly imply that you've at least somewhat adjusted your opinion, without having to explicitly bring it up.
Of course, it also wouldn't have spawned a hundred-comment sub-thread.
It's bloody hard to express something sincerely on the internet without sounding like you're just being sarcastic.