CATAN
When can you exchange a Helper card?
One reply from the publisher's staff gives the main rule, and the answer follows the Helpers rulebook where the reply's last point is unclear.
- RedPiranha · Community · 2014-07-20
Only after you have used it, and right away that same turn. You can't exchange a Helper you haven't used. Per the Helpers rules, after using a sun-side Helper you either exchange or flip it, and after using a moon-side Helper you exchange it.