You want to press deeper.
What type of GL accounts are you posting to in the J/E(s). I ask because I would recommend leaving the prevent flag, but you would have change your calendar back to last year, period 12. Your method would work too. But if you have and P&L accounts, you better recalc account balances, before you run any financial statements for the current year. This is my reason for always changing the calendar. I automatically recalc account balances after change in calendar. If you don't your period balances will be wrong on P&L accounts, Balance sheet accounts are accumulative so no problem.