The RTM and the retail release are one and the same. No differences, zero, nada, etc. The nag screens are probably asking you to activate your version of windows with a legal purchased key. If you fail to do so, your RTM (same as retail) installation will stop working or go into a reduced functionality mode, eventually. So the answer is you don't have to reinstall anything but you have to get a legal key if you want to legally activate your copy of windows 7.