Can't Change App Permissions for First-Party Apple Apps?

Hi there,

I have been attempting to customize my Mac by changing app icons and came across a strange problem.

While using traditional methods, I've had no issue swapping out icons for third-party apps, Apple's (especially the built-in ones) refuse to cooperate.

Essentially, I don't have permission to modify anything in regards to Apple's own apps (including the icon, of course). When I try to change permissions, after clicking the lock in the bottom right of the "get info" window, I get an error message: "The operation can't be completed because you don't have the necessary permission."

I finally, magically got permissions changed for Final Cut Pro X, but have had no success with any other Apple made apps to date.

Any thoughts or suggestions would be appreciated, thanks!