As a follow-up to [this post], here is a real-world example of where we wanted to override document metadata: 

The issue is that when Notes documents are created with Anonymous forms, they may not contain the usual $UpdatedBy field.  Since Notes Migrator for SharePoint uses that field by default to determine the author and the last modifier of the document, the migration jobs did not work correctly on these documents when the "Preserve Created/Modified identities" option was selected.  Thanks Matt, for coming up with a workaround using our cool new 5.0 feature:

Fortunately, in the 5.0 version, you are able to provide overrides for these fields in your job's source data definition.

To migrate this database, you can add two new fields to your job's source data definition; the field to override the author should have the alias {OverrideAuthor}, and the field to override the last modifier should have the alias {OverrideLastModifier}.  (It's important to remember to use the "curly-brace" characters in these aliases).

Both of these fields could be of ColumnType "Formula".  The formula for {OverrideAuthor} might be something like this:

    @if ($UpdatedBy = null; From; $UpdatedBy)

The formula for {OverrideLastModifier} might be something like:

    @if ($UpdatedBy = null; From; @Subset($UpdatedBy; -1))

In both of these example formulas, the data in the "From" field is used when the $UpdatedBy field doesn't exist; you may want to choose a different field, or even provide a specific user name as a replacement.