PRS-T2 how to make update file

Hi,
is there any guide about how to make *.img file for prst2?
i want to add RTL to my reader
these are the steps:
extract firmware from my device (odex file)
deodex it
add RTL to the firmware
odex it
insert it again to ereader system

but i don't know how to update the system after editing the firmware file.
so i want any guide to help me doing this