Looking for some input and advice on a situation that has arisen in the game I'm running.

Through a series of convoluted Rogue Trader-ey events, the explorers have indebted a Necron Cryptek with great resources. Each of them has requested some kind of boon as thanks for the assistance they provided to him. Most of it's simple stuff like Necron weaponry, or Necron augments to existing equipment, that sort of thing. What brought me here is the request of our Heretek rogue trader who has been in constant pursuit of immortality-through-machine body: She requested biotransference as the Necrontyr of old.

Setting aside the obvious socio-political consequences of pouring once's self into a living metal shell in the Imperium, is this even a thing the Necron are capable of doing anymore, and if so, what would even be the effects of doing so if I decided I wanted to take that plunge?

No expert, but I'd say it isn't. The Necrons have some crazy High Science at their disposal, but they didn't do the biotransference to themselves; their Star God masters did, with their ability to actually alter the facts of reality, and the necrons repaid this treacherous deed, wherein the souls, minds, and consciousnesses of most of their race were lost, by shattering the C'Tan, and locking those bits up. The Necrons can no more make other people into more Necrons, if you will, then they can transmigrate themselves back into fleshy bodies; something certain portions of their people, and their fluff, seem very interested in doing. If there were people who wanted the mechanical bodies, and they'd be willing to let the Necrons use their organic bodies, since they wouldn't be using them, at that point, that would probably be a plan some Necrons would follow, but, as I said, I don't believe it is within their power, and most of the Necrons can't even think, I suppose, since their higher functions were lost, either in the transference, or on account of the millions of years in stasis, with Windows Vista. Your Rogue Trader would also have to fear that his mind might do like theirs, and not survive, intact, or that the Cryptek might leave code inside, that will render the RT at his control, under certain circumstances. Even under the assistance of a legitimately good person, it is quite perilous, and nothing says that this Cryptek is actually nice, honorable, or fair. This is 40k, after all. Does your Rogue Trader know any Blood Angels Astartes? That might help.

On thing the Necrons COULD do, possibly, however, would be to augment, and I use that word humorously, because by the time it is done, you might be like one of the characters out of Ghost in the Shell (three brain cells, concealed within a human-mimicking robot body, the supernatural capabilities of which are potentially rangeless), and with the Necron's science, and a combination of healing nanites, and the resurrection protocols, be nigh-immortal, in flesh, and tech. I'm sort of imagining back when Pariahs were still a thing. They were organic, to start with, and heavily modified with Necron components. If the process had been continued, and the GeeDubs people not canned them, when they Tomb Kings in Space!!!! ed their fluff, they might've become even more tech-integrated, and become like "true" Necrons. What the Necrons CAN do has limits, and what one WILL do, regardless of the help given, even more so, but a degree of what you're asking MIGHT be possible. Of course, this is mostly my opinion on the matter. Good luck.

Well, let's see. The vast majority of Necrontyr that entered those metal bodies became slaves, so...

I'd reduce the player's WP to 0, make them into a Null, and give them regeneration. I'd request they speak with a mechanical voice whenever possible and try to agree with any and all suggestions the other players make, especially when those statements contradict each other.

Seriously though, I think Venkelos has it covered. It probably isn't within current Necron capability. I have some reservations with the entire theory, though, since IIRC Flayed Ones and Pariahs are later renditions of the Necrons that were perhaps created after the C'tan were broken up into pieces.

All makes sense! I wasn't sure if the C'tan merely taught the Necron how to do the process and just taught them wrong, or if they were an integral part of the process in and of its self. The consciousness part wasn't as much a concern since my understanding was that the presence or lack of previous personality had a lot to do with the quality of the body prepped for the upload (aside from those degraded over time in the "modern day" or infected with the flayer or destroyer plagues)

I'll probably just be going with the necron sponsored cyber augmentation.

Well, let's see. The vast majority of Necrontyr that entered those metal bodies became slaves, so...

I'd reduce the player's WP to 0, make them into a Null, and give them regeneration. I'd request they speak with a mechanical voice whenever possible and try to agree with any and all suggestions the other players make, especially when those statements contradict each other.

Seriously though, I think Venkelos has it covered. It probably isn't within current Necron capability. I have some reservations with the entire theory, though, since IIRC Flayed Ones and Pariahs are later renditions of the Necrons that were perhaps created after the C'tan were broken up into pieces.

I'll be the first to say I'm not entirely up to speed with the "current" Necron fluff. I was a bit grumpy with the reboot, and never bought the codex, so I am limited to what I've read online, and to what of that material carried over into Deathwatch, in the form of the Outer Reach. Thus, anything I say needs to be taken with a grain of salt. As for the "Flayer and Destroyer Plagues", my take on them was always more of a second Vista joke; they became code, and without proper maintenance/oversight, the code developed glitches, "viruses" if you will. I also wouldn't put it past the C'Tan to have implemented them as a fail safe; even the most arrogant, vain master, who could never possibly see themselves being toppled, or defeated, always seems to have that ONE "just in case" scenario, and without the C'Tan, maybe the Necrons were supposed to devolve into Destroyers, Flayed Ones, and other, even worse abominations. Having faulty systems maintain them, down throughout the millennia, also didn't help. Even a Phaeron's code was damaged, and he should have had the best firewalls, INSERT OTHER NEEDLESS COMPUTER TERM HERE, and all, to keep his core personality in place.

Yeah, I might just go super-cheese; give him a number of ranks of Machine, maybe 6 (Necrons are usually 8, if I recall, but plenty of Tech-Priests get some, and don't count as full robots), the benefits of several high-quality pieces of cybertech, and maybe, if you really want to, give those parts self-repair, as finding a repairman could be hard.

The main point I would make is that this would NOT be a reward, that it WOULD have strings attached, and that those strings WOULD be those of a puppet and master.

Yep, oh so very much so. If I'm a Necron of any stripe that can still think, I know I'm a robotic demigod, of sorts, who once battled gods, alongside my own, and then turned on my own gods, shattering GODS to pieces, before existing for millions of years, with access to "science" that can challenge some of the greatest achievements of warp craft, for cheesery, and with less chance of being betrayed by the source. I might let a little Human think I'm doing him a favor, but he'll get off no more easily than if he had gone to a Chaos Warpsmith, and said "hey, can you make me into an immortal Man of Steel?"