Bipolar does mess with everything. You're absolutely correct. There are still minor choices, even under the worst of brain chemical imbalances, that will help to change outlook. My therapist does try and everyone at the hospital tried to ingrain that in me. I can still choose to be happy. I can rarely just get over it, when I'm in the fog of depression, but I can do things that being me Joy anyway, because they will still feel good and will still give me good brain chemicals.
For an example... Working out releases all kinds of happy chemicals. When I'm even on the edge of hope and half gone, I still force myself to go to the gym. I might cry my way through a yoga class or for a couple miles on the elliptical, but I do feel better when I'm done, even though I'm still somewhat depressed. It's not as bad as before I started.
A yoga friend today was talking about how she felt so embarrassed being upset over someone she loves getting very close to death, and knowing it will be soon. She said she had tears in her eyes when she got there late, and said she cried through class. I saw that the tears were still there after. We talked a few minutes and I gave her a hug. She thanked me and told me she never knew yoga could make you cry that much. I explained that it's done that to me many times. She felt better afterwards though. And I could tell she did.