Please pardon the late reply. I've modified the plan to two months each for a gratitude journal, cold showers, meditation, and cutting sugar. Thank you for sharing your own experiences!
Cold showers: I'm curious about the distance between how people swear by them and the inconclusive research - and, like you said, there's no obvious harm. When I've done them in the past I've noticed an energy boost in the hours afterwards, but I've been unable to push myself to keep them up when autumn hits. So this will be a summer experiment.
Sugar: I once cut sugar (all sweets, though not all added sugars) for roughly two months and felt like I noticed the disappearance of big energy drops. This time I want to see what else comes of it.
Gratitude journal: Given the research behind it, this seems obviously worth the effort, and is what I'm doing right now. It seems like there's evidence that writing 1-3 times a week gives better results, but I'm doing it daily for the habit formation.
Other than that, I don't have much to reply beyond appreciating the personal reference points, the meditation links, and the encouragement!
I got some good ideas from this list, and will report back with results.
Most of these seem like hacks to increase extroversion.
For #12, shouldn't three star reviews divide (one star + five star reviews), not be subtracted?
This is helpful, thanks! Do you have a study or post in mind?
This seems correct to me. There are already self-improvement approaches to attempt and modify. Using epistemic rationality to achieve instrumental rationality is less about creating an RSI, and more about evaluating and improving upon existing SIs.