If you have change notification function then it must be easy to implement, or else possibly if log in fails you can prompt for the credentials again.
Just persist the value on Registry or as a file, and make use of it each time a login is required, and when it fails on a try just prompt for it and over write the persisted values.
this is just a way of doing it, modify it as needed and have fun.
private void LogTheUserIn()
{
string credentials = GetPersistedCredentials();
bool loginFailed = TryConnectToServer(credentials);
if (loginFailed)
{
credentials = PromptForCredentials();
OverWritePersistedCredentials(credentials);
LogTheUserIn();
}
}
Hope it helps.