So I'm in technet, and I was wondering if I install Server 2k8 R2 on my server with key, will it transform into the retail version of Server 2k8 r2 when it is officially released or will I have to reformat? I am very eager to try it out, and I know I could try it in a VM, but I want the real experience. So just wondering.

You will probably be able to upgrade the RC to the Retail version after it is released.

Hi, It is not guaranteed that you will be able to upgrade from Windows Server 2008 R2 RC version to RTM version directly. Generally speaking, it is recommended that you perform clean installation when the RTM version is released. Thank you for your understanding. Tim Quan - MSFT

Right, there are no guarantees.And, of course, if you are running a DC, a parallel install with DC promotion-demotion is really the only good way to go.