Make any bespoke harmonization logic more prominent than it currently is

[abradyGDIT]

Any value augmentation/transformation that isn't directly data-driven -- i.e. anything not "substitute value X with harmonized version Y", like "Add to CDA metadata: all IDC file records have format='DICOM'" -- should be prominently documented so that invisible or hard-to-find transformations don't cause tracing/comprehension headaches.

This will probably ultimately result in a document to be maintained in the harmonization repo, but first: catalog all such things currently in operation following a full review of the harmonization layers in the ETL code.