I’m not a lawyer but this seems questionable to me. The fact that Trump is factually residing there doesn’t mean he is legally residing there. See my example of somebody living in a storage unit.
So here are the issues as I see them:
Is the agreement legally binding in government matters? I feel it is. One of the parties to the agreement was the town council. And the agreement was used as the settlement in a court case. So it has official recognition beyond being just an agreement between two private parties.
Did Trump agree in 1993 that he would not live at Mar-a-Lago? The newspaper article says Paul Rampell, Trump’s attorney, said Trump was agreeing to this.
Was Trump’s 1993 agreement not to live at Mar-a-Lago legally binding or was it just a voluntary decision on his part? The article seems to be saying it was legally binding: “The deal he struck made it clear that no one could live permanently at the property.”
Does living as a guest at Mar-a-Lago for three weeks a year legally qualify the location as a place Trump can declare as his legal residence? I don’t know Florida law well enough to answer this authoritatively. But the article says they asked Ronald Meyer, who is an expert on this subject and he said that position was questionable.
If a person is living at a location in a manner that is in violation of a legally recognized agreement, does this mean the person is living in that location illegally? I feel it does. I don’t see how you can argue that you are legally breaking the terms of a legal agreement. Civil law is still law. You’re doing something illegal by breaking a civil law just as you would be by breaking a criminal law.
If a person is living in a location illegally, can they claim the location as their legal residence? Again, I feel that illegality negates any possibility of claiming legality. You can’t claim you are legally doing something that’s illegal.