The ease of this "just" is the most concerning thing in the context of humankind's survival.

Right? I wouldn't expect genes for heat/cold tolerance in other organisms to necessarily be useful in humans. They work by mechanisms that are useful for that organism, but humans have our own set of problems.

It's like saying you can strap a jet engine on to a tractor and expect farm work to massively speed up. No: the machinery doesn't translate for a clean swap like that.

Then I recommend you don't find out what "Project Molecule" intends to do.