The password you use to login, is your password.
The security code is a one time thing which is sent to you when you login on a new device. It expiries after a while and you get a new one if you try to login on a new device.
Never give anyone your password or your security code. The security question might be asked by support if you contact them. Never give it to anyone else (not what the question is nor the answer).
When you change your name, the creations you have uploaded now, should still be created to your old name (YOB..) but you could also just download them, remove them from the gallery and then re-upload once you changed your name. You will loose all current downloads and like though. They won't be given to just someone else.
Maybe it is best to leave as is. You are not at any security risk with just the Origin-ID/EA-ID showing in the gallery.