HT1918 iTunes does not allow me to change my account information so that I can be able to make payments for applications.

Question

iTunes does not allow me to change my billing information. I have a problem with my current credit card so I want to use another billing option.

Answer 1

The iTunes Store in a country is intended only for use by that country's residents, and only while they are in the country. To use the iTunes Store in a country you need a credit card (or other card type if acceptable in a country) issued in that country, billed to an address in that country, and also be physically present in that country when using the store.  You are also restricted to waiting 90 days between country changes.
E.g., "The iTunes Service is available to you only in the United States, its territories, and possessions. You agree not to use or attempt to use the iTunes Service from outside these locations. Apple may use technologies to verify your compliance." - http://www.apple.com/legal/itunes/us/terms.html#SERVICE
In general, switching countries is not easy and it is only intended you do it if you really are moving residence.
Purchases made in one country do not carry over to another country, though you can still use them as long as they are on your computer.  You cannot, for example, update apps purchased in another country.  I have things I bought in stores in Europe.  I can continue to use them here in the USA but I no longer have access to those stores to buy replacements now I live here.  In the case of apps and media each country has its own licensing contracts and this is the way Apple has it set up to work.
Your specific"cookie" error may relate to you trying to use an iTunes store from outside that country and part of the "Apple may use technologies to verify your compliance".