Yes, just slightly open the door to stop the current cycle. Wait for the water to stop dripping before adding what you need. Then make sure to press the start button to have it continue with the current cycle when the door is closed. If you don't press the start button, it will not continue when the door is closed. Make sure you don't press the on/off button. This would cause the cycle to stop.
The start button is on the right and the on/off button is on the left.