Yesterday we ate the three leftover onigiri I'd made last week and frozen following Biggie's method. I then re-heated them in the microwave (Took 2 minutes; one minute each side. I don't know if that's normal but I wanted "piping hot". I left the plastic wrap on them and reshaped/squished - Ouch!Hot! - before removing plasticwrap) and we ate them, they tasted fine and not yucky or hard or anything, and none of us have suffered from violent food poisoning. So I am a confirmed paranoid nutter where food safety is concerned (And yet you should see the state of my stovetop - it's shocking.)
But really - caution is best, right?