As part of 6.2 to 6.4 net new upgrade process I need to update latest uber file in parent pom and some java files. All I have is compiled Jar file and I don't have source code. Is there any way to update files in jar file and recompile.
You would run into issues where API contracts have been modified or deprecated even in case you reverse engineer the code. You'd need to have base project setup files (archetypes/library versions etc.) which are missing in this case.
How would you even identify what library version is being used and what should be the new version to make it work in 6.4? You'd definitely need to have the source code.