Whilst updating my work machine I've come to realise that I've installed a kernel from the unstable debian distribution, rather than testing. I must have added unstable sources to get something else working (probably NVIDIA).
Now, I'd like to roll back to testing if possible. You can take the configuration from one kernel and apply it to a newer one using the command make oldconfig (which only prompts you for things introduced since the last .config was written).
I wonder if there's a way of doing make newconfig, for when you've installed a newer kernel by mistake?