AA's computers process equipment changes like this, and it can be all over the map. Sometimes you will keep the same seat number, i.e 8A stays 8A, sometimes you'll get an equivalent seat, i.e. aisle to aisle, and other times youll go from say a MCE aisle to row 100 middle. There's certainly no standard protocol, although if the same seat number is available you will usually end up there, although not always.