You should not attempt to do this on a device that does not have a recovery, because if something goes wrong you may have to reinstall your rom (not very likely though). You should probably back up SystemUI.apk You should also have some experience modding and some experience using Apktool and Linux.
If your having problems modding SystemUI.apk on JB then this thread is just for you. I recently found out how to mod the Jelly Bean SystemUI. Jelly Bean has made it very difficult to mod. Yes it is still easy to replace images, but if you want to do some major changes to the UI such as a 100 percent battery mod or changing the status bar color then you will need to know exactly how to do it. For example, if you get the UI decompiled without errors and you recompile it without errors YOUR RECOMPILED SystemUI.apk WILL NOT WORK and your status bar will disappear etc... There is a special way to get everything working and I will show you how.
Before we start I recommend that you have File Roller: one of the most popular archive managers for Linux (Ubuntu comes with it). If your distribution uses a Debian package manager (most popular ones do) then all you have to do is go into the terminal and type:
sudo apt-get install file-roller
sudo apt-get install openjdk-6-jre
Before we start, you will need 7zip and java. Just search and you will find the programs to install
Now we will install APKTOOL. You may already have it installed BUT your version will probably not work. I have ran around the internet for a modified apktool that wont give you errors (If you follow my directions). I came across a great thread. check it out and download all the tools their (dont forget aapt) http://forum.xda-developers.com/show....php?t=1755243. If you are in Linux rename the jar file to apktool.jar and move the the jar plus aapt to /usr/local/bin. You will need root. If you are in Windows rename the jar to apktool.jar and move it and aapt to your WINDOWS directory. You also need zipalign http://powerpoint45.webs.com/android/zipalign(<Linux)( zipalign for windows:- ZIPALIGN )move it to your WINDOWS dir/bin dir. You need one more thing. It is from the apktool websitehttp://code.google.com/p/android-apktool/. According to your os download either apktool-install-linux-r04-brut1.tar.bz2 or apktool-install-windows-r04-brut1.tar.bz2. Extract the contents. You only need one file from the archive. In linux move apktool (not apktool.jar) to /usr/local/bin. In Windows move apktool.bat to your WINDOWS directory. Dont jump ahead and say "Now that I got apktool set up, I know what to do", because it gets a lot more difficult than you are used to using apktool.
Now that you have apktool set up, you need to know how to mod SystemUI.apk. Get SystemUI.apk from /system/app within your device onto the computer. Now make a backup of SystemUI.apk on your computer because we will NEED it later. So you need two SystemUI.apk files on your computer. You could name one “backup” if you'd like. So now now we need to decompile the apk. Go into the terminal/cmd and cd/chdir into the directory you have SystemUI.apk. Now type
apktool if SystemUI.apk
apktool d SystemUI.apk
This is the part where you start modding. You can make many customizations to the UI this way as you probably know. I will just show you how to make a 100 percent battery mod. You need to go into the decompile folder (SystemUI) using a file manager, Then from SystemUI, go delete res/drawable/stat_sys_battery.xml and replace it with http://powerpoint45.webs.com/android...ys_battery.xml (to download that file right click on link and click something like "save link as"). Now you need to move to a new directory: /res. In that folder you need to look through all the directories that start with the word drawable. For example drawable-mdpi. There is one directory that your device uses for images but you may not know which one. Your device might be MDPI but use drawable-sw600dp from the UI instead of drawable-mdpi. So if you dont know or you want to be safe then search through the drawable folders and if their are any battery icons then remember you will need to add 100 battery icons to each one of the folders with battery icons. The battery icons are the ones named something like stat_sys_battery_0.png. So if you need to add 100 icons they need to be named in numerical order from stat_sys_battery_0.png to stat_sys_battery_100.png. Dont worry though, you wont need to rename 100 icons. Their ar many battery mods online that you can get them from, but I have some images you can download: http://powerpoint45.webs.com/android...RY_BLUE.tar.gz. Download it, extract it and copy all the images into all the drawable folders that contain battery icons. Now your ready for compiling; The step that is different than how we have always done it before Jelly Bean existed. keep in mind that some images can not be changed or edited at all durring this step because it will result with many errors durring compiling. You would have to add images to the archive after its compiled
Like I said at the end of step 4, this step will be different than you have seen before. This is also the step where you will be using File Roller/7zip. To build the apk make sure you are in the terminal in the directory where SystemUI exists and type:
apktool b SystemUI almostdone.apk
in and type
zipalign -v 4 allmostdone.apk done.apk
Now you install the apk. Their are many meathods of installing the apk, here are a couple. Transfer done.apk to your device and rename it to SystemUI.apk. Now use a root browser or terminal app to replace the other SystemUI.apk on your system at /system/app. And make sure you give it the same permissions as all the other apk's in the system/app directory. Then reboot. Or you could make a flashable zip to install it.