Being against illegal immigration is just code for xenophobia. Trump just used xenophobes to get elected by playing to their fears. The truth is that people who are against 'illegal' immigration are really against all immigration and they want to put more limits on legal immigration. Anyone who really wanted to stop illegal immigration would allow more legal immigration.
Immigration was one of the principle issues on which Trump campaigned and had he adopted a softer position his core supporters would have embraced other candidates. This wasn't a minor issue, or some footnote. This issue was the reason for his success. By turning his back on his supporters, he's undermined the legitimacy of his nomination.
Have you forgotten, he's a businessman. This is just business on a political scale. It seams like too many people don't want all the illegals deported to the extent he may not get elected. If he doesn't get elected, he can't do anything about it. Basically it's the same position but more appealing to the public.
In my opinion, I think we should deport all illegals. Even ones with children born here. Granted, legally we can't deport the child that was born here as they are U.S. citizens, but there is a solution. Basically give the parents a choice. They can either put the child up for adoption and be deported or elect to give up their child's citizenship so the family can be deported together. Problem solved.
Trump's position was crazy and unworkable. Although he risks alienating his base,he can't win with minorities, Hispanics and women with the kind of rhetoric he has been spouting. It is not practical for him to have kept to his original position. There will be plenty of people in his base who are angry, but the really rabid ones won't leave.
I feel that Donald Trump is allowed to change his mind a million times as long as he is working to make America really exceptional. We are a caring country, a loving and accepting people, and if what Donald Trump changes his mind to is in alignment with our core values then he can change his mind all he wants.
If Trump is beginning to see the unfairness of his former hardline position on immigration, that speaks to his willingness to listen to other sides and adapt to new information. I don't believe, however, that this shift is anything more than an attempt to stop his nosedive in the polls.