I tried creating an Image with a JellyBean's LatinIME.apk, replacing ICS's LatinIME.apk, in system apps folder of ICS ROM, but it crashed. But when I put it in
preInstalledApk folder, it got compiled and ran successfully.
But it needs to be selected from "Language and Input" in Settings and also both the keyboards have same name.
What I want is to install JellyBean's LatinIME.apk during compile time of Image and also be the default input method. I don't mind if its not a system app. And I will change the ICS's LatinIME.apk-Keyboard name from the code, so that user can selected any of them without scratching their heads.