Well, sure. In theory, he could do anything by fiat within the bounds of established regulatory discretion. Of course, I wouldn't worry too much about all of the stuff that "Trump could do" until he gets around to doing it. He talks a lot. And, I suspect he won't have time to do all of the stuff that people worry about him potentially doing... As frustratingly slow as congressional action is -- it's more resistant to…
This is not a fair assessment. Plenty of people learned that lesson a long time ago, but always get laughed out of the room by the party in power.
I remember in the aftermath of 9/11 when GWB made one of the largest executive power grabs in history, and the right-wing whole-heartedly supported him in the name of keeping us safe. A common refrain from my left-leaning friends explaining why this was a bad idea was "Imagine someone like Hillary Clinton with these powers." Of course, that was all hand-waved away until Obama took office, then suddenly "executive overreach" became such a hot topic.
The only way to change the momentum of the executive gaining more power over more things is to convince both the in- and out-of-power parties that giving the President more authority is a bad thing. Good luck convincing the in-power party of that, no matter which side of the aisle they sit on.