It is highly unlikely that Osirix modifies the original DICOM images. You can check if the comment is included in exported images by importing them into Slicer and checking metadata content (by right-clicking on the the image in Slicer DICOM browser and choosing “View metadata”).
If comments are not exported to DICOM files then you can read it from the DICOM database of Osirix. Many years ago they used sqlite database for this (maybe the still do), which can be easily read in Python.