I'm considering a mutant character who has regeneration but, due to a friendship with an inquisitive techpriest, has a number of interesting implanted and boinic technology (as the techpriest likes the fact he can practice messing about with a living patient with no real worries about messing it all up and killing them)
I'm trying to think of a way to represent his body attempting to reject the implants, and possibly expell them from his anatomy. I'm considering something along the lines of having to pass a test every time an area with bionics/implants takes damage or have them expelled when the area heals itself, but I'm not sure what test should be rolled =/
Does anyone have any ideas?
Alternatively, you could look at regeneration as just being a supercharged version of normal human healing - faster, but not capable of repairing things a normal human couldn't. In other words, just like humans can heal a cut, but can't re-grow an arm, there's no reason that a regeneration has to include re-growing limbs or organs.
Of course, regeneration can include re-growth of limbs (or even in the case of one of my characters, return from death), but it doesn't necessarily have to.
In other words, no need to do anything - other than a note that you can't use of regeneration to recover bionic locations.
I'd go with Marco's idea, personally, but if you really want to be regenerating everything, right up to the rejection of implants, then there're probably a few ways you could do it. I'd guess that you do want the full regrowth version, judging by your character background int he other thread.
The simplest might be to have his implants change from game to game, or between campaigns. This would represent the rejection over a long period, which would be sensible.
Otherwise, you could have it so that every time a Regeneration roll is made, he must fail a Toughness test or start rejecting the implant - taking d3 or so damage to that location until it is crippled, at which point it begins regrowing as the original human/mutant part, and you Regenerate the damage as normal.
Of course, this makes certain implants (bionic lungs, eyes, brain... Anything in the head or chest) a really bad idea, so it might not be the best way to do it.
I'm not really sure if this would work so well, since I'm not familiar with the Regeneration ability in-game and don;t have my books with me, so if someone could polish this idea up, or kick holes in it, that'd be helpful.
In the case of psychically driven regeneration, as opposed to alien healing rates or similar (and which applies to a particular mutant is entirely down to the story of the mutant in question) then it is quite possible that there would be minimal, if any, issue with the cybernetics.
Because the Warp "self" is driving the change it should be possible (through psycho-conditioning, hypnotherapy...etc) to engender an acceptance of the artificial parts sfficient that the Warp "self" actually assimilates them. I would be careful about that to avoid stepping into territory which might preempt Necron stuff but...
On the other hand, if the Warp "self" rejects the artificials then (as is likely to happen with Alien healing rates...etc) it is important to consider the way in which an amputated limb (for example) behaves.
As part of the process of healing after amputation blood vessels which are no longer required to bring blood to and from the extremity die back, retracting somewhat back from the stump. Muscles, no longer being worked by the mass of the extremity or the activities associated, atrophy. Nerves which are no longer being used die off and are reincorporated by the body.
The issue comes when these nerves are connected (by whatever means) to some form of cybernetic. Quite quickly I would expect the subject to lose the use of the limb as his body rejects the neural connections which drive it.
Whether this is followed by the artificial "growing out" to be replaced by a fresh "natural" is entirely your concern though.