Is "android_secret_code" a code to unlock the SIM? On my Sony Xperia E, I copied and extracted my SIM unlock app (the official one) and found a bunch of 7 or 8 numbers with the words android_secret_code.

Is this my SIM unlock code? If so, just to be safe, does anything happen if I get this PIN wrong?
No, android_secret_codes contains a list of dialer codes to enter hidden menus. It is typed in Dialer to enter those hidden menus (they are usually in form of *#-------#).

You need the PUK Code (PIN Unlock Key) to unlock your specific SIM card. You can get PUK from your carrier network. You can call them and get the PUK once you verify your identity.