Is rotating seat post 180 degrees to get a tri position a good idea?
I ride my bikes HARD (BMX park/street/dirt) and back in the 90s we had to use what ever parts we could find. Since no one was making parts back then for BMX, it was usually MTB parts. Even back then and with all the abuse we put them through, (yes, even flipping seats and posts backwards to fit our needs) the parts seemed to hold up pretty well (Except the hollow axles used for quick release, those snapped pretty easy), about the only thing was the posts would kink, but that was because they were raised way high and dropped from 30-40 feet up off the ground. I can't tell what brand of post that it, but it looks more solid than the crap we used back then, and we beat them up pretty good. My guess is that you will be fine.