Hi Hugo,
Sorry for the late reply. The past is a weekend.
So I think what your mean is this: Start exposure, then if you meet the problem, close the external shutter to stop the light, but the exposure of the camera is still running, after the problem is solved, open the shutter until the exposure of the camera is over. Am I right?
If I am right, I can not help you. Like I said, the camera is always exposuring, there is only a difference in light. It is impossible for us to exposure but do not receive the light.
Thanks
Chad