I need to change the security questions/answers in my Appleid, but my rescue email address is no longer valid and I can't change it.

You need to ask Apple to reset your security questions; ways of contacting them include clicking here and picking a method for your country, phoning AppleCare and asking for the Account Security team, and filling out and submitting this form.

They wouldn't be security questions if they could be bypassed without Apple verifying your identity.

This link will provide the assistance you need: http://support.apple.com/kb/ht5312