Can you use the add-ons for fallout 3 game of the year edition to add them to the normal fallout 3

The Fallout 3 GOTY edition is basically the normal edition with the downloadable content. I'm pretty sure you have the option to omit and add DLC's, so you should be able to add the extra content with the installer, that is as long as both your version and the GOTY versions are the same (not 100% sure about this). You can patch the game after all is installed and it should work fine.