I TAKE NO RESPOSIBILITY WHAT SO EVER IF YOU BREAK OR BRICK YOUR PHONE
MAKE A BACKUP COPY OF EVERYTHING BEFORE YOU START
First, extract the following folder from /system/priv-app/Launcher3/Launcher3.apk (Copy the APK to somewhere else first):
/res/drawable-mdpi-v4
That folder contains all of the launcher icons. Remember the filenames of the icons that you want to replace (i.e. allapp_att_deviceunlock.png).
Then copy /product/overlay/Launcher3-overlay.apk and open it in an APK editor.
Make a new folder in /res called drawable-mdpi-v4
Put the icon (only png) that you want to replace with the filename of the original app’s icon (i.e. allapp_att_deviceunlock.png to replace Device Unlock). I would recommend that you only use circle images. Squares look really ugly.
Repack the APK, make sure it’s named Launcher3-overlay.apk, and replace it with the apk in /product/overlay.
Restart device
You could put apps on the launcher by changing the package name of the app you want to the name of an app on the launcher. You can’t have 2 apps with the same package name in the system, so if you want to put an app in the place of the browser, you have to remove the browser.
Main Menu:
Phone: com.android.dialer
Messages: com.android.mms
Contacts: com.android.contacts
Gallery: com.android.gallery3d
Music: com.android.music
Camera: com.tcl.camera
Browser: org.chromium.chrome
Settings: com.android.settings
ATT Device Unlock (not on some phones): com.att.deviceunlock
Cricket Device Unlock (not on some phones): com.cricketwireless.deviceunlock
(If the Launcher3-overlay from your phone does not copy into your phone use this Laucher3-overlay Caution: if you use this one the up button will not work anymore to open up the apps)
Credits to @FliphoneBochur