We use MarcEdit primarily to deal with ebook records, which sometime have thorny 300 fields. We want to standardize these fields as much as possible while preserving valuable information. Adding a 300 field to every single record is quite easy – see this page for information.
However, some batches will be mixed; some records will have 300s and some won’t. In this situation, we’ve opted to add a generic 300 field to records that lack one completely. This involve just the smallest amount of conditional logic.
This adds a 300 field only to records that don’t already have one.
Reformatting physical descriptions to be appropriate for ebooks is more difficult – but possible using MarcEdit. More details forthcoming.