"I respect you as you are, and support your desire to change. :)"
I feel like I've been looking for this statement for years. Sometimes I'd get half of it at a time. I'd say, "It won't affect my opinion of you," or "I love you," or "I don't care about that." Or I'd listen to what the loved one wanted to change, and try to offer helpful suggestions. But these were all failures to some degree.
After writing it, I immediately thought of a dozen times in my life when this is what I was trying to say.