Recently, I bought a pack of miso paste. It contains 1kg, far more than I actually need. Is it ok to freeze what I don't need? If so, how long could I keep it frozen?
You can freeze it, however using it will be a problem as you will have to chip out what you want on demand rather than thaw and re-freeze it.
Miso paste lasts ages in the fridge as long as you put it in an airtight container to prevent it from drying out, you're better off just doing that.
Freeze it in an ice tray for ease of use. My jar says it lasts 6 weeks in the fridge so feel I should freeze it.
Miso should still remain malleable when put in the freezer, it's actually the recommended way of storing miso. It's the only way to keep the flavour from changing.
Source: Japanese Style Originator「和風総本家」 - Episode 23 on Netflix
I store my miso in a plastic zip lock bag (mine comes directly from a supply store and comes in plastic, not a container) in the freezer. It stays pretty soft and I can easily get it out with a measuring spoon without any problems.