Would you be able to put "nem" first?
"Nem ez egy alma."
does that make sense still? Would that mean more like "No! It's not an apple!" rather than "It's not an apple."
You can't put 'nem' first this way, but there are some other variations: Nem, ez egy alma. - No, this is an apple. Nem ez az alma (hanem az). - The apple is not this one (but that one). / Not this apple (but that one). Ez nem az alma (hanem a körte). - This is not the apple (but the pear). Az alma nem ez. - The apple is not this one. Nem alma ez, hanem körte. - This is not an apple, but a pear.
There's more, but I'm gonna stop here :D