What can you functionally change in the construction of a damper? Valving and duty duration till fade? Dampers are a wear item, so ARB, TJM, Opposite Lock & Pedders make money selling dampers to replace worn units, and sometimes selling "upgraded" units to the kind of people who think a shock absorber will give them "a bit more" lift. Just like they sell heavy duty torsion bars so people can lift their cars, which Zordo also agrees is unnecessary. To acheive a lift, you only need (NEED... want is different) to change your damper valving from the thoroughly tested factory valving to a different valving if you have increased or decreased the unsprung mass of your vehicle.
People like Zordo are in the business of making money, that's fine, we all are, but someone has to come out in favour of keeping their money in their pocket. In reality if you're selling a "lift" kit for a Navara, all the kit need include is a modification to the rear springs (helper or extra leaf or extended shackle) and lengthened rear dampers if desired.
An aftermarket suspension "upgrade" kit can include new dampers, but that's not what the OP wants as far as I can tell.