you cannot replace an odex.. odex are encrypted for a specific firmware. they also are extensions of an apk. you need both.. you would need to de-odex and then replace the deodexed file.
I though they were just byte-optimized for a particular phone so upon boot it doesn't need to create .dex's and just loads the .dex from the odex directly (in turn giving u a faster boot, at the sacrifice of customization).
HTC has been quite good about releasing expedient Android system … more
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?