Yes, you will need to flash the whole de-odexed rom again.so you are saying that there is no need to install the whole rom just only that de-odexed file
if yes then where is located that de-odexed file?because i do not know
actually when you are saying install do you mean i place it in the appropiate folder and reboot the device?
edit: wait! i realized something else!by de-odexed file do you mean the rom?
if yes then if i install it and restore the nandroid backup will it remain de-odexed?
But you cannot restore a nandroid backup because that will overwrite the entire system, and back to an odexed rom.
Basically, after flashing the de-odexed rom, you will need to install & configure everything again.
But if you have Titanium Backup, it can helps you to backup/restore "user" apps (and their settings). In that case, you will still need to configure everything related to system apps, such as all your accounts, home screens, lock screen, etc.
After you have a de-odexed rom running, you may install any Mod designed for Sensation (provided that the version is supported by the Mod).
And there is no difference, in terms of user experience, between odexed and de-odexed rom.