Ok i find this very strange, but choose an emulator, PJ, 1964, mupen etc and then set the desktop to what ever res you want it and save it. Now load a rom and watch the emulator in Window (Desktop) mode keep it's original browser diamater (shape) while the TR64 emulated screen will what you set it to. Now to have the menu and staus bar change to the TR64OGL one you have to click it out of focus (click the desktop) and click back on the emulator. See image below
