Best way to update overlay data

[J. Riesmeier]

What is the background of your question: do you want to store the modified DICOM image as a new SOP instance / DICOM file afterwards?

[J. Riesmeier]

You could use the DicomImage class e.g. for extracting details on the overlay planes of an existing DICOM image, but since the main purpose of this class is "image display", it is not really suited for storing DICOM images to a file or dataset.