I have switched to Japan store many times without even being asked for "a credit card", which is not the country I live now. And I have completed multiple purchases using switched account.
I feel glad that Apple does allow us to switch between multiple countries to experience contents available only in other countries.
When you sign up, just click "none" in credit card section, and you will be good to go, unless iTunes store in USA DOES force you to assign a credit card to continue. This is not even an issue in Chinese store, which you DO need to have a bank card available in China to purchase items not provided for free because you need to add money to your ID first (no gift card available in China)