One of the ideas I'm mulling over from this study of ancient Greek philosophy is this: Instead of using willpower to get through things you don't like, you can learn to appreciate the things that are good for you or gradually move up through activities that you enjoy and that are a little better for you than what you were doing before.
I've been trying this idea in terms of exercise. Having decided that I would be the type of person who exercises, I've been keeping up this habit for a little over a month. I usually run with W-. He treats those sessions as recovery runs (he's much fitter than I am and can run circles around me), and I treat them as "extra time with W- and an occasion for smugness." I'm not yet at the point of experiencing the runner's high, but I do feel somewhat pleased by this ability to keep up with the heart rate thresholds that should help me build up endurance. I've even gone for runs on my own, propelled by growing custom and the knowledge that I'm going to be able to celebrate whatever progress I'm making. Gradual progress through the Hacker's Diet exercise ladder is fun, too.
In terms of food, I'm finally beginning to appreciate the sourness of yogurt, the peppery taste of radishes, and other things I'm still not particularly fond of but can deal with.
As for substitution, keeping a range of nonfiction books in the house means I'm less inclined to spend time playing video games. Latin and Japanese flashcards on my phone mean less time reading fiction. A file full of writing ideas means less time spent browsing the Web.
We change a little at a time. It's good to pay attention to your changing tastes, and to influence them towards what's good for you. Sometimes you can kick it off with a little bribery or willpower, if you use that temporary space to look for more things to appreciate. Sometimes you can encourage yourself by making better activities more convenient. Good to keep growing!