I don't think a country would make BTC its own currency.
But they might recognize it as a foreign currency or even recognize every Cryptocurrency as just another foreign currency.
They wouldn't need to define how it works in a law, since they also don't define how another country is printing its money.
Yes, but the foreign country defines how it works in their own law, so it is legally defined somewhere.
(Again, not looking to debate if a country would make BTC its own currency, purely an example)
I don't know, if countries really have a list of "approved" foreign currencies, I guess they don't.
But assume they have: Do they kick out a currency, if a foreign country chances their laws?
So, if we speak of the code of a cryptocurrency as the law of that currency, a country wouldn't care if that code changes. (wasn't that one of your initial questions?)
They would have to define things like, what exchange rate is used, how you have to tax gains(income), what records you have to keep and have to give to authorities.
I don't see, how they would have to legally define anything regarding the code(and its changes) and I don't know of any familiar examples in already existing laws.
Countries do have such lists. They serve different purposes and are approved by different ways by different groups.
Again it is a local variable.
Some #import the BIS lists for purposes of Foreign Exchange.
http://en.wikipedia.org/wiki/Bank_for_International_SettlementsIn the USA, I can take Rubles, Euros and Yen to my bank, hand them to a teller, and they will credit my account for Dollars.
I can also make any exchange with any of these with a willing recipient.
In California, Bitcoin is considered "Lawful Money" by the state, but an Asset, by the Fed. So these are taxed differently, even though it is just one tax form that goes to state and fed. It gets complicated to follow all the rules.