If you use insert in the spreadsheet to load the monthly historical rates by using FBDI, the existing historical rate for a specific ledger, currency, account combination, and accounting period will be replaced by the new rate. This is because the insert action will overwrite the existing rate with the new rate in the GL_HISTORICAL_RATES_INT table. If you want to preserve the existing rate, you should use update or delete actions instead. References:
* How Historical Rates Import Data Is Processed, Section: Use the Historical Rates Import file-based data import (FBDI) template to import historical rates from external and legacy sources to Oracle General Ledger
* Import Historical Rates, Section: Details
* Entering Historical Rates, Section: Entering Historical Rates