You should be cautious about performing any activity other than reporting when you are using a reporting currency. This is especially true of entering or importing new journals into your reporting currency, since journals are only converted and replicated from your ledger to your reporting currencies - not the other way around.
Caution: Entering new journals or changing existing journals in a reporting currency can make it very difficult to reconcile the reporting currency to the associated ledger.
Generally, you would consider entering new journals or changing an existing journal in a reporting currency when you need to adjust the balances in a reporting currency because the jurisdiction in which you report those reporting currency amounts follows different accounting rules than those you use in your ledger.