Can I post to a period prior to my latest open period? Are the balances rolled forward? Is retained earnings updated?

When you post to an earlier open period, actual balances roll forward through the latest open period; budget balances roll forward through the end of the latest open budget year; and encumbrance balances roll forward through the end of the latest open encumbrance year. If you post a journal entry into a prior year, General Ledger adjusts your retained earnings balance for the effect on your income and expense accounts.