I am about to do my first tri, and I have a road bike with aero's. I was talking to a guy at the LBS and he said that modern seat posts can be rotated to achieve the same forward positioning that is achieved with modified seat post such as the one from profile, that give a simulated 78 degree positioning. I have a Bontrager Race X Lite seat post, is this true, can it actually be rotated? Or will the seat never be level, or will the carbon have forces that were never expected in the design?

Yours can be rotated and will be fine, but just because it's modern doesn't mean it can be(i.e. my Ritchey cannot be rotated and it's only 6 months old).