The following workflow should be possible. One reason is that a user who accidentally saves manual segmentation work as nrrd , though needs DICOM SEG, it should be possible to fix.
NOT READY FOR MASTER!
Already add serialization of properties marked as persistent to the multilabel nrrd writer. Also copied the code from image nrrd file reader to get all properties while reading a nrrd image (not nice but works). But testing was only for one use case. So looking for side effects before merging this commit (6f1b022e7b8d) into master.
The second commit is to syn the referenceFiles property while reading the nrrd file. I think that is not necessary, if the serialization of StringLookupTableProperty works properly. In the future we shoul get rid of this property anyway.
Some hints for this use case:
T25988: LabelSetImageIO should support time geometries and property serialization copes partially with the same problem and shows what have to be done to allow LabelSetImageIO store all relevant informations into NRRD (and load them again).
I don't know the status of the branch above as it is dangeling arround for quite some time.
But if this task should be done in a sound way (as @metzger proposed above) we should do the following / build upon other tasks (because lot of the problems must also be solved to handle rewriting of DICOM SEG (T26953)):
Then it should do the trick. ;)