Your oauth_token and oauth_secret will change every time you re-authenticate with the OAuth flow. Your client keys, however, always stay the same. You can get around having to reauthenticate every time by simply saving the 4 string values, and using them for your applications.
However, if you are using multiple user accounts, you will get a separate oauth_token and oauth_secret for each account. Authenticating a new account will not invalidate another account's keys.