Not a lot has changed from what I can see. Don't worry you can still stack Mfg. coupons and DG coupons. The only change I think I see is that they will NOT give cash back on a purchase if you use coupons. Honestly that does not bother me, I think that stores are supposed to not give cash back. If you read most coupons they say that you are not supposed to get cash for them, sell them, etc.
Here's the link if you want to check it out yourself: http://www.dollargeneral.com/OurStores/Pages/CouponPolicy.aspx