DICOM tag value changes after resaving

I modified a DICOM tag from a DICOM image that has an embedded color lut (photometric interpretation = PALETTE COLOR). When I resave the DICOM image with the modified tag the photometric interpretation is changed to MONOCHROME2, therefore the image is shown in grayscale rather than the original colors when viewed in a DICOM viewer. I am using the

 'CreateMode', 'Copy'

argument which preserves the whole original header except that specific tag. How can I preserve this also?

Thanks.