Hi Dave,
Thank you for reaching out and we hope you are in good health. We appreciate your interest in Samsung home appliances, specifically with Samsung - Smart BESPOKE Linear Wash 39dBA Dishwasher - Navy steel.
Yes, you can open the dishwasher while running and add more dishes. After loading new utensils or dishes, close the door and press start to resume the cycle.
I have shared the user manual link below. Please access the link and turn to page 34.
https://downloadcenter.samsung.com/content/UM/202105/20210503134711859/MANUAL_USERS_DD68-00209A-04_EN_MES_20210406.pdf
Please feel free to communicate with us through the channels below if you have additional questions.
1. Facebook Messenger: http://m.me/samsungsupport
2. Twitter: https://twitter.com/messages/compose?recipient_id=18768513
3. Samsung Community: https://us.community.samsung.com/t5/Samsung-Community/ct-p/us
Your reference number: 1144529087
Leo