If we could somehow give a thick atmosphere to Jupiter's moon Ganymede, could we live there?

Still not enough info to give a proper answer. There's more to sustaining life than thick atmosphere.

It would still be way too cold. The atmosphere would freeze solid.

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It would have to be an extremely cold atmosphere to keep it from evaporating away because Ganymede has a low surface gravity. It's a bit warmer than Titan, so it'll lose atmosphere faster and since gases absorb heat it'll warm up the atmosphere by itself and "evaporate" even faster.

So while not strictly impossible, it would be a sisyphian task of sorts.

Not unless you have a portable fusion reactor to give you enough energy to survive there. and a earth-like environment in which to do the surviving