Wait, I was totally joking. And no, a neutral drop is when you rev in neutral and drop it into D. Never do this O_O It's awful on your transmission.
If you want your transmission to last long, let it be in the highest gear possible, which is pretty much what it will try to do in D, for efficiency, but it's also the least stressful since the engine will have the least torque and rpm. Also, hard driving will heat up the transmission, and if it's really beaten on, the overheating could reduce life. Same goes for drifting, burnouts, or any sort of wheelspin due to the change in wheel speed when it goes from slip to grip, bringing a shock on the trasmission.
I don't think double downshifting is that harmful if you are only doing it during spirited drives. It'll put more strain on all the parts but the electronics that control our transmissions won't allow it to overrev, which is good. But you shouldn't use the engine braking from downshifting to brake. It's less predictable and causes more stress. Brake pads are MUCH cheaper to replace than a new transmission ($200-300 vs $7000+).
If you really want to help lengthen transmission life and power capacity, a transmission cooler and valve body upgrade would really help it deal with forced induction.
A small tip: to avoid any jerkiness in manual mode, keep your pedal position steady throughout the shift. So if you are cruising, don't mash on the gas halfway through the downshift.
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