Changing region

I don't believe that there are any region-specific aspects for an iPod, you certainly shouldn't have to (re)activate it for another country, I have iPods that were bought in the US and used in the UK, and vice versa, and never encountered any issues - all I needed to do was change timezone setting so that the clock is correct 😉

You will find, though, that access to the iTunes Store is a different matter - you'll need to have a credit card issued by a US bank and associated with a US address. I believe that it should be possible to do this with an existing Apple ID previously used in another country - assuming this to be the case you should definitely do that so that you retain full access to previous store purchases.

iPods manufactured for EU markets have built-in volume limiting, as required by the EUSSR's commissars. You'll have to search around to see if there are any hacks to remove this, though I suspect that its built in to the hardware rather than being controlled by software settings.