I'm guessing that you can't because picking the weapon(s) you want is already time consuming enough. Including the ability to change attachments mid-game would be too much incentive for players to remain idle at their command posts in my opinion. Not to mention all the sub-menus that would probably have to accompany that.

watching this video http://www.youtube.com/watch?v=OpsIRohaH_4 at 6:33 you can see the weapons menu. it actually looks like we will have loadouts bc looking at the gun icons closely shows that theres ablities with the guns.

also @wraith i saw you talking earlier about the clip size for the .50 cal, its 4 shots for sure since fireing the gun breaks the ammo circle icon into 4ths (you cna see it at 0:15), it might have 16 bullets in reserve though.

From gameplay I've seen I'm 99% sure that you can't.

One.

are you sure?
big limitation in a game renouned for its array of customisation

Erm, not really a limitation... you customise a gun how you want, use it when you want, and if you want to change it then you can. Just not in the middle of a game so you're not wasting useful team-time.