Available since 1.0.0 version
Repeating Issues add-on allow to edit custom field values when setup repeating actions like Clone Issue or Create Sub-task. To edit custom fields please clicking on "More..." link on repeating issue dialog - this will load all available custom fields that can be edited for given issue type.
Only custom fields added to screens for given issue type will be available for edition
All custom fields will have simple form input where static value or dynamic value can be provided - see Velocity Template Language in Repeating Issues add-on.