Run Android app with the System signature key

Hi all,

I recently switched mobile phone operator and the new operator has taken on my old number. However, the number stored in the SIM, which is visible to Android, is incorrect (it is the number that was given to me before the switch over).

Somebody wrote a little app a few years ago that allows changing the number on the SIM:

https://github.com/fommil/MyPhoneNumber/blob/master/src/org/lytsing/myphonenumber/MyPhoneNumber.java

I have no idea how the original author ever got it to compile, I've needed to use reflection much as others have discovered:

http://stackoverflow.com/questions/9369648

but there is an additional problem: apparently this must be run by an app signed with the "system signature key":

http://stackoverflow.com/a/6029410/1041691

Now, this is the closest documentation I can find for signing an application in IntelliJ:

https://www.jetbrains.com/idea/webhelp/generating-a-signed-apk-using-a-wizard.html

http://stackoverflow.com/a/3651653/1041691

So how do I run an app on my phone (which is physically connected by USB), signed with the system signature key, in IntelliJ? (e.g. how do I obtain the system key in the form of a keystore, should it be that simple)