Actually people in China nowadays are afraid of Muslims who are in black robes, veils or with long beards, especially in other provinces other than Xinjiang. People will get away from them. It is no discrimination and you can not force people to overcome their understandable fear. So I think it is also a better choice for Muslims not to wear like that, if they really want to get along well with the majority in China.
I believe there should not be a problem for Muslims @ there respectable locations to abide by the law. As long as its the law which is imposed on the entire community and not just the Muslims. If it is something which helps the city improve their security and make them feel more secure which is kinda silly over long beards, veils and black robes even though black robes raise a security concern I believe the ones who do wear them should know very well to expose there identity when it is needed around for example a Bank.
Again even in Canada it would be kinda silly if in my community there was someone who had a long beard and because I reacted to long beards and have got fear of them that the person who has got his own belief would have to shave it off because of my fear. And that you can not have me overcome my fear but it is alright to force it upon my community member to shave off his beard instead.
Even if there seems to be a ban I believe it is more logical and reasonable for it to be temporary as long it helps the city investigate the crimes. It is not likely that the criminals will still not commit crime with there beards and veils gone.
If you think about it.. if it is about security concerns.. Wouldn't it really be easier to locate and investigate 1 certain person who stands out in his veil, long beard or black robes and who seems to be unique out of a group of people.. then some one who blends in with the community without the long beard,veil and black robes and still will commit the same crimes as before. They just made there job harder o_o