I had a problem that seemingly quite a few other players had or have: An Xbox Live account based in a country, then I moved to the US and I cannot change it in my account profile, meaning I cannot buy points or products or whatever that can only be used for an account US-based from the beginning.
Well actually it seems that there is a way around, not a total answer to the problem but at least a partial one. Meaning, you can keep your account, even if the country no longer is the one where you live, and purchase products from the original country of your account (in the currency of that country obviously). This works at least if you are now in the US. You just need to use a debit card instead of a credit card.
Example based on my case: XBox live account based in France, now I am in the US. I bought points in EUR using my US debit card, and purchased a game extension with these points. The extension is available both in FR and in the US.
Perhaps it does not help anyone or that was already known, but since I have not been able to find this answer on the forum, I thought it would be worth writing.