How should I go about transferring Neopoints to a side account (and back again)? I would like to earn the Soup Faerie avatar, but I want to make sure I don't do anything that's going to get my account flagged or frozen or anything. Is there a specific "Give So-And-So X Neopoints" command somewhere, or do I have to sell myself something ridiculously overpriced on the Trading Post or something?

Just set up a trade on your side account and offer as many NPs as you can (max 800K per offer). There's no need to complete the trade; the NPs in a trade don't count against your total.

Also, to make it a little easier, you can make multiple offers for the same trade.

I personally transferred all my NP over to my side via an auction, since I had ~4.5 mil. It did take me a couple of weeks to get the avatar though, because I waited until my pets were starving to feed them, and it took a few tries. You can open a bank account on a side to store your NP and keep it safe, just as long as you don't collect any interest on it.