Reading around a bit it looks like there isn't going to be an executive order issued to implement the President's policy announcement. This will make it more difficult for opponents of the policy to figure out where any legitimate legal challenges might lay. Opponents will have to look for changes in actions, agency by agency, and make a case for the changes being unlawful. Opponents will have to do this for each action they deem unlawful. This will require a bunch of work, lots of time, and the ability to establish standing. In other words, by the time a challenge is perfected and brought to court, President Obama's term will be over. Working on legislation might be a better use of time.