It's not impossible to brick a NC, but as long as you can boot off the card slot, it's unlikely. (There is no fix for a device that is truly bricked, unless you can send it in to the mfgr.) What is possible is that you can create a situation that you (and I) wouldn't know how to resolve.
I gave away my NC years ago. It's waaaay too slow for my tastes. (Not enough cpu and ram.) Check out my devices on the left. All 3 are running a Jelly Bean rom (CM10 or a variant). From what I've seen, the NC can barely run CM7, and CM9 or CM10 is just waaaay too slow.
These days you can buy a cheap tablet so there's no need to convert a reader to one. My recommendation is to buy a Nexus tablet (although my HP Touchpad with CM10 is nice too).