Allowed? Hmmm....not sure it's a matter of being "allowed" or not but it's probably in the best interest of US that their planes be changed over to OneWorld as quickly as possible. Probably a mixed bag from StarAlliance's viewpoint as they get free advertising as long as their logo is still on the planes. Then again they may take the point of view that US is no longer part of their system and therefore not ought to make it look like they still are. Quite frankly I haven't paid that much attention to other changeovers but I do recall some strangely, and obviously makeshift, labeled planes. There was some Continental metal that showed up here at SAT that was relabeled but it looked more like a teenager with a sack of spray paint and a bad stencil did it.