To recap: you want a minimum-handwaving solution to this list of synthskin properties. Much will depend on how much you're prepared to pay, in storyline terms; these properties will have causes, and consequences.
- It can be reconfigured by an artist using some kind of nano-manipulator brush
This is the easiest part. The newly gengineered skin cells may have chromatophoric properties, possibly as part of their other functions. I.e. you're looking at a differentiated cell layer with different cells optimized for different properties. When the "acid resistant" cells emerge from the inner lattice and expand to seal the upper layers, the skin color and texture becomes that of the acid-resistant scales.
- The synth skin can filter nitrogen bubbles from her blood, giving her an advantage when diving or changing atmospheres.
Also "easy", even if this will have a high metabolic cost, in that we know how this might work. Also you can't just alter the skin, this requires modifying capillaries too, to achieve sufficient blood flow. Your "skin" will need specialized cells containing nitrogenase enzymes, and convert molecular nitrogen to ammonia and then to uric acid; then you have the problem of getting rid of the uric acid. If you're doing this in a marine environment, it would be easy to get rid of ammonia through an osmotic membrane open to the seawater. The main problem is that ordinary nitrogenases aren't fast enough - you'll need both a rete mirabile-like layer below the dermis to supply reaction surface area, and a nitrogenase family of enzymes based on unobtainium instead of commonplace iron, vanadium or molybdenum.
- She can withstand sulfuric acid vapor in the atmosphere (like the cloud deck of Venus) with only a gas mask (small emergency oxygen mask?), long enough to perform a physical activity outside that would kill (or severely burn) everyone else.
Heh. This requires the skin to not rect with sulfuric acid, which requires it to have a sealable layer of very unreactive substances; unreactive substances (and here you're looking at nothing less than tetrafluoroethylene) are a copper-plated bitch to synthesize, and you need a completely different biochemistry to handle them. Or you don't use a virus and go the full nanonic assembler way. Possibly the virus can construct an organic Waldo factory that assembles inorganic nanobots, and all the necessary machinery to produce PTFE-plated cells.
Another, less tasteful possibility is the secretion of a protective oily mucus. This can be done within the limits Earth biochemistry, but its resistance to sulfuric acid is not absolute. The slime of course must not be water-based. It would also explain why she only can do this for "short" periods however.
- She can't get drunk or high, at least not for very long before the skin filters it from her blood.
This could be a byproduct of the nitrogenase filters in the blood. They will also work against carbon mono- and dioxide, and against alcohols. Can't have them doing too much though, or it will interfere with the respiratory reflex.
- Synth skin cells eventually "die" and must be replaced with new seed injections of the nano-virus into deeper skin. Most of her synth skin however is damaged in one incident, exposure to cold, and is replaced with new and improved™ synth skin. She spends about 9 months in medical suspended animation while it regrows.
Well, this could explain the acid-resistant coating - it's not biologically produced at all, must be supplied ready-made from the outside. Regrowth would never last nine months however; in that time, the skin has time to die again by itself.
- She improbably survives (<1 minute) inside an electro-plasma magnetic foundry fusion doohickey thanks to the Leidenfrost effect or a plasma double-layer or maybe an electrostatic sheath.
This last is less unlikely than it seems: electromagnetics don't work on biological creatures unless you set the power setting to 11, and plasma sintering could be easily counteracted by the same insulating layer that gives acid resistance. Death for a normal human would be mainly provoked by a mixture of vacuum exposure and electrocution.
You cannot very well use the Leidenfrost effect because you'd need an ablative layer which wouldn't last more than a few seconds, and not in a vacuum anyway (and you can't have plasma effects in any reasonable atmosphere, unless you employ really high power levels - "lightning strike" or "nuclear detonation" levels). Electrostatic sheath is marginally possible but it would require a sizeable organic capacitor or other power source, which can't be supplied with synth skin. Unless your girl is going full cyborg; also, any technological power source would contain conductive metals or even ferrous metals, and would require a significant shielding to be able to work inside a plasma chamber.
I think that passive insulation (and a not too unreasonable chamber power) is the best you can reasonably expect to be aiming for.
UPDATE: if by "electro-plasma magnetic foundry fusion" you are referring to a Tokamak-style hot hydrogen fusion reactor, then NO. WAY. Sorry. Not with synth-skin, not with anything else. No ordinary matter can survive there. You would need a magnetic shielding strong enough to disrupt the fusion bottle, and this would result in a massive explosion or, more likely, in the whole reactor being SCRAMmed in as few milliseconds as inhumanly possible by the best security systems money can buy. A disrupted magnetic bottle with multimillion-degree plasma going amok is definitely something you don't want when you design a reactor. Also, such a reactor would be impossible to power up with someone inside, to boot.