What exactly is framework-res.apk
Framework-res.apk basically contains the elements of the Graphical User Interface for the phone. This file is available at /system/framework/framework-res.apk. 

Poking in this file would mean changing the complete look and feel of your device. Since it is the main element of your screen, replacing it directly by pushing it through ADB would lead to soft-brick. Therefore, this apk should carefully be modified and replaced using the recovery module of the phone. 

Check this link for details on the same: Modifying the framework-res.apk (Theming the UI)