I don't think you are born with different wiring to the three different kinds of cones, your brain just learns to lump all the red ones together, so that a red object stays the same colour in different parts of your visual field. The claim is that the monkeys learned which of the previously-identical cones now had a new colour.
Do they lose any sleep philosophising about how these new colours are possible, and what to call them? Who knows. But I believe they can still do all the usual monkey things.
That's the point they can not distinguish more colors. Their retinal cones still have the same spectral response. They cannot distinguish between a normal 500nm green leaf and a 900nm infrared source.
The monkeys are in a different study, the one I linked a few posts above.
The nanoparticles sound to me like they could be safer? Would be interesting to know whether they can be non-uniformly spread, so that only half the green cones can see one.