I'm logging an improvement request on behalf of customer as per following:

• The mapping between source and target fields can be defined in the configuration (e.g. source field xxx -> target field yyy).
• The mapping between source and target values can be defined in the configuration for enumerations (e.g. source option "abc" in field xxx -> target option "def" in field yyy).
• For mandatory target fields that have no source equivalent, the user should be able to provide a target value at copy-time.
• For optional target fields that have no source equivalent, it should be possible in the configuration to define whether the user can or cannot provide a target value at copy-time.

The way to think of this is that the plugin is similar to the jira import tool, which allows you to map from columns to fields in a fairly flexible way.

The mapping also has to be per field configuration scheme, since it may be different for projects/issue types with different schemes.

SAC:
https://support.atlassian.com/browse/JSP-150131