Radiation is a severe problem for the Galilean moons except for Callisto. You could probably live metres underground on Ganymede to be adequately shielded but you'd have to arrive and leave very quickly. Only a few days on the surface, or in transit on a spacecraft, would result in a fatal dose of radiation. That's not the kind of problem that you can work around with genetic engineering. Even on Callisto, radiation is over ten times higher than on earth but at least its gravity is 0.13 G.

The non-Galilean moons are all tiny—at least four orders of magnitude less massive—with the surface gravity on Himalia only 0.006 G. Better to choose one of the dozens of larger asteroids which avoid the complications of Jupiter's gravity well.