suggestion
take a look at this url, and examine the zip file contained.
you could boot into cwm and install the zip (not suggesting, its what i did)
if u make a zip file in the same layout you could install your zip and it will update the system partition.
as you have a desire, heres whats required
on phone: place phone into fastboot mode
on computer: unzip to a folder , place the img file in such folder,
open a command prompt, (navigate to folder using the cd command)
and type: fastboot boot bravo-cwm.img
mount sd card, toggle usb storage, place your zip in root of sdcard.
then untoggle, go back, select option to install zip from sdcard.
choose select zip file.
find your zip.
tap on the file, and it will install...
you SHOULD by this point have an updated phone as you desired (lol)
if it does not work as you expected, have a look for a standard system.img for your phone, and put that into a zip
name the zip (i put it in caps, weather needed i dont know) PM99IMG.zip
place it into root of sdcard, and put phone into the first screen of recovery menu, the white screen.
it will analyze your zip and ask you to install, press up to flash and then the required option to reboot when its done to revert your phone back to normal.
hope this helps there buddy,
ill most likley forget to check back, so if u need any help pm me and ill see what i can do,