I have a 2009 Accord with about 122k miles. I have always used conventional oil but recently I had the car to the dealer for a recall that involved replacing engine parts and oil change. However they used synthetic. Do I need to always use synthetic oil for all future changes?
The spec for a 2009 Honda Accord is plain old oil; no specific need for synthetic. As long as you get your oil changed regularly, it won't be breaking down to the point where the difference is measurable (except in your wallet). You won't have any problems switching between synthetic and non-synthetic.