So making changes for both me and her isn't good? I'm still trying to understand this mentality. I'm also still reading DR. If I understand correctly, things that I do for her might not stick, if she comes back, because if I get her back, I will have reached my goal, and won't perhaps feel as much motivation to keep doing whatever it is. Is that right?
I think you misunderstood. You make the changes within yourself for YOU and you only. Never make them on the hopes of winning someone back.
Think about this - let's say someone in our situation works very hard and makes all the changes that they think will bring the person back - only that it doesn't. So, all they are left with is the bitterness/anger towards the ex and within because they feel all of it was for naught. And that is no reason to do it.
There are moments in this life when you are so confident in the rightness of your actions, that not even for a second do you consider the option that you might be wrong.