Bought some aged (3 years), artisanal miso today and the clerk suggested I store it in the freezer. (reito in Japanese) I had never heard of that before and asked to make sure that I had not misunderstood her. "Reito" for freezer not "reizo" for fridge.
She said that it will keep much longer in the freezer. And that unlike storing it in the fridge, the color will not change (sometimes you will notice that with miso that sits around in the fridge).
She said that when you want to use it, just spoon it out. It will not freeze like an icecube but should maintain some malleability.
I am going to give it a shot - but wanted to pass on the tidbit to fellow chowhounds.
Cheers from Tokyo!