Reapply to a postdoc position that I rejected before?
What do you have to lose? Worst case scenario is that you are rejected. I don't see any possible downside here.

Anecdote: This was not for a postdoc position, but for a research internship: I contacted the researcher who I wanted to work for not just once, but three years in a row. All three times they expressed interest. The first time, it was too late so they said to apply next year. The second time, they were going to give an offer, which I turned down. The third time, I felt mildly awkward, but I knew that this was a position I still really wanted -- so I simply explained as much, and thanked them a lot for their interest in previous years. It worked and I got the position again.