Autos can flower on 18/6 as well as 12/12. Flipping it back to 18/6 won't cause it to hermie unless you go back and forth to 12/12 and 18/6 several times. Which will cause it to stress. Its your choice to pick which one 12/12 or 18/6. 18/6 means more light, more GROW but bigger light bill. 12/12 can still grow but it will have less light to peak its potential.
Hey Growmie,
No, once you flip it to 12/12 you leave it there, turning it back could cause the plant to hermie. Hopefully, I answered your question and remember Happy Growing and Free your mind one puff at a time.