Tune it? Harry hadn't known he could do that, though if Draco said it, it had to be possible. Separating his emotions from the memory was something he didn't know if he would be capable of doing, however, even if it was technically within the realm of possibility. It took a while, but Harry eventually lifted his gaze back to Draco's and started to square his shoulders, before the charm hit him again.
The wall of mailboxes didn't last as long the second time, despite Harry's readiness. Fear at what else Draco might see, his worry, helped Draco along.
Harry’s scar burst open. He knew he was dead: it was pain beyond imagining, pain past endurance –
He was gone from the hall, he was locked in the coils of a creature with red eyes, so tightly bound that Harry did not know where his body ended and the creature’s began. They were fused together, bound by pain, and there was no escape –
And when the creature spoke, it used Harry’s mouth, so that in his agony he felt his jaw move….
“Kill me now, Dumbledore. …”
Blinded and dying, every part of him screaming for release, Harry felt the creature use him again. …
“If death is nothing, Dumbledore, kill the boy. …”
Let the pain stop, thought Harry. Let him kill us. … End it, Dumbledore… Death is nothing compared to this….
And I’ll see Sirius again. …
"NO!" Harry didn't know how he'd done it, but a door in his mind shut so abruptly that he could almost feel it slam. His head suddenly aching, Harry continued to push against his awareness of Draco's mind though it was no longer in his own. He hadn't been expecting the results.