Right now I've got film in my 690, but I'm wondering whether once I'm done I can keep the back open and run through all the shutter speeds. I always do this with other cameras, but it's just something I've never tried with this camera.
Back open or closed, will the counter on the bottom still advance if there's no film moving through the camera?
Yes, the counter will advance. The counter is connected to the shutter release button through a rod. It's not a film roller or frame gear mechanism moving the counter.
It's easy enough to reset the counter. The bottom pulls off easily, then the counter comes out with two screws. Pick a number!
I seem to remember that you HAD to open the back door to fire the GW series without film loaded?