Can I change the photo of the bed during the 8-hour session?

This is possible.

At the bottom right of the photo you uploaded, you will see the edit icon (a pen). Click on it to change the photo. If you want to continue the session with a better photo or in a different bed, you can upload a new photo to the quantum network. After the quantum entanglement is complete, as indicated by the 100% upload progress bar, you and the MedBed can continue.