Several things to think about.

1st and formost. If you are working to a Procedure... Polarity is an essencial variable and to change it you will need a new WPS.  Simply changing polarity for the sake of  convenience may put you out of compliance with the code you are working to.

AC has been used with E7018 as a last resort in cases where no other action will eliminate Arc Blow, or when an AC power supply is all that is available.

DCEN (or the straight polarity side of the AC half cycle) will reduce penetration with your stick electrode... This is only an advangage in sheet or very thin material (usually E7018 is not selected for sheet).

I know AC open roots with E7018 is common in Skills USA competition projects (no code restriction)