Den ersten Teil der Frage hat sich erledigt. Ich habe in der englischen Dokumentation folgendes gefunden:
Zitat
The solution is to tell KMyMoney that the transactions are the same, using the manual matching interface. This allows you to match an imported transaction with a hand-entered (non-imported) transaction. To do so, select one of the transactions to be matched by clicking on it, then select the other by left clicking on it while pressing the Ctrl key, and then select Match from the context menu. This changes the background color to a pale green. This will match and combine the two transactions together. The values of both transactions must be the same for the match to work, except that the dates may differ by the window specified in the settings, as described above. If you are happy with the result, right click the matched transaction, then select Accept.