Policy changes happen at every level of government all the time, that isn't a valid defense for illegal activity that has been generally not enforced. But risks are known.
I should note that I am not defending the policy per se, I am pointing out that immigration policy has been a mess for a long time. The new sheriff is changing policy, there are unintended consequences, but it should be noted that they didn't create the mess. Also, no intelligent conversations are being had on the issue, just a shouting match between two sides which will never be productive.