No, you cannot.
"Nicht" has to go after "die Lampe"
"Nein, ich mag die Lampe nicht" and "Nein, die Lampe mag ich nicht" are both correct.
What he means by emphasis is just that you're 'stressing' the object you don't like by placing it first in the sentence.
It could be used to express extra dislike for the lamp, or maybe dislike for this particular lamp. But no matter what way you order it, "I don't like the lamp" is the fundamental translation
That sentence is already reversed. "Das Mädchen (Akkusativ) mag der Junge (Nominativ)." The girl is liked by the boy. The standard order would be "Der Junge mag das Mädchen." If the girl likes the boy, the standard order is "Das Mädchen (Nominativ) mag den Jungen (Akkusativ)." reversed order: "Den Jungen (Akkusativ) mag das Mädchen (Nominativ)."