You may have to plug and re-drill the screw holes in the neck
and sand the heel a bit thinner or widen the neck pocket on the
body a small bit, but apart from that, it should fit.
You will need a new nut, since the S neck is 1mm wider than the
neck. You'll also need new tuners, unless you want to mess
with the 540 headstock, since the way the tuners are mounted
on the JS100 is different to the way they're mounted on higher
end models (including the 540).
btw, unless I missed something, if it's a square heel neck it won't be a prestige.