If you used regular oil the first year semi-synthetic the 2nd and then just synthetic oil in a 2001 I4 Honda Accord can you go back to regular oil?
Yes, you can with no problem.
Virtualy all oils, synthetic & conventional, are interchangeable.
Honda specifies the use of genuine Honda ATF Z1 only. Any substitute may cause shifting problems. I would not use any other fluid period. Synthetic may be fine but I am not 100% sure so my advice is stick with Honda ATF Z1. You can ask your Honda dealer, but if he say use synthetic get it in writing or your warranty may be void.
SAE 0W-20 any major brand. As 0W-20 weight oil is only manufactured as a Synthetic oil you will have to purchase Synthetic. I highly recommend Pennzoil Platinum Full Synthetic which is what I use in my 2013 Honda Accord. Purchase a 5 quart jug to save money. Your Honda will take 4.5 quarts. Also purchase a quality oil filter and change the filter when you change the oil. Change your oil when the oil minder…