Springs alone can be changed, but if going lower on the standard shocks, they will wear out more quickly due to the difference in damping rate. It's not a hard job to do yourself with the right tools and some springs compressors. Especially on such a new car where the likelyhood of the bolts being seized is low. It might be a good time to get him into a bit of diy mechanic-ing?
Coilovers are even easier to change as you replace the whole front strut at the front. Coilovers are better but more expensive.
At the rear, I'd imagine the C2 is trailing arms although I'm not 100%. If so, you drop the arms, take the old springs out, compress the new ones, put them in, bolt the arms back up and undo the compressors. Or you can put them in without compressors and jack the arms up.
