android - Create System Application

Question

What I should to do to create a system app (to obtain rights to use android:sharedUserId="android.uid.system"in manifest file without receiving an error from package manager about certification problem?

I use rooted phone with stock firmware.

Answer 1

Ok, I think that I find sollution from great xda developers: http://forum.xda-developers.com/showthread.php?t=1776095 here is full description how to obtain access to apps signed by platform keys. Do you apply with this approach?
PS it is interesting that users from stack instead of investigating hard problem immediately say that you can not solve it, then reduce novice user's reputation...