How to migrate MediaFile custom fields?

The method MediaFileK13.FromReader() doesn't allow for Media File custom fields.

I am migrating my K13 media files to Content Items and need to migrate a custom field I have called PhotoSource.

Do I need to overwrite FromReader after each git pull or is there some other way I can get these custom fields?

public static MediaFileK13 FromReader(IDataReader reader, SemanticVersion version) => new(
        reader.Unbox<int>("FileID"), reader.Unbox<string>("FileName"), reader.Unbox<string>("FileTitle"), reader.Unbox<string>("FileDescription"), reader.Unbox<string>("FileExtension"), reader.Unbox<string>("FileMimeType"), reader.Unbox<string>("FilePath"), reader.Unbox<long>("FileSize"), reader.Unbox<int?>("FileImageWidth"), reader.Unbox<int?>("FileImageHeight"), reader.Unbox<Guid>("FileGUID"), reader.Unbox<int>("FileLibraryID"), reader.Unbox<int>("FileSiteID"), reader.Unbox<int?>("FileCreatedByUserID"), reader.Unbox<DateTime>("FileCreatedWhen"), reader.Unbox<int?>("FileModifiedByUserID"), reader.Unbox<DateTime>("FileModifiedWhen"), reader.Unbox<string?>("FileCustomData")
    );