You can probably avoid the Rough Beast atoning you against your will with sufficient moral purity.
Abadar can atone you to LN, because Abadar is Judged LN: if you do the things and only the things which a mortal Abadar would have in your shoes, Pharasma's court will send you to Axis regardless of what you pinged as in life. Abadar is the best to know whether you're an Abadaran, so He can manually update your detectable alignment to match your eventual Judgement. Abadar can also atone you to an alignment within a step of LN (otherwise Abadaran paladins would have to find a cleric from outside their church to cast the atonements), but for the God of Walls and Ditches to be the authority here you'd have to be an Abadaran kind of LG. (But again, atonement isn't necessary unless you need it for your divine casting class, because again, an atonement doesn't change your alignment - only what you read as. If you can atone to LG, you already were LG.)
If you're not particularly the Worldendingy kind of Chaos or Evil, I don't think you have to worry... or rather, I don't think you should worry about it before you worry about, like, lightning. When the Rough Beast smites you, He'll probably use lightning. Atonement is kind of weaksauce as a weapon, I think?