Hmm..after mucho deliberation I have come up with two possible theories of why Al is cosplaying Ed.
He is either trying to do just that and make people think he IS Ed in order to use his idendtity to get information and do reasherch. In the trailer we see him doing alchemy on what looks like the armor so..he may be trying to complete the image by controlling the armor. It's a very good disguise if u ask me...I mean only the few people in the military who knew Ed closely would notice (like Roy and Riza) that it wasn't Ed, and even fewer people know what happened to Ed and Al in the end of the series.
OR he got all his memories back at once and couldn't handel it so he went a bit crazy @_@!
I don't know....call me crazy!! I just think there is REASON behind Al's new Ed look. Being a copycat just for the heck of it or whatever just doesn't seem like Al... ^_^;;;
SO what do ya think? Aggree? Disagree? Got another theory?