I am seriously looking for some good tool to avoid the labor work.
I read the article which mearly has the list of differences and it has guide to migrating flex 3 project to flex 4 even this talks just about manual migration.
Is labor work inevitable in flex migration?
Since no one has answered except commenting, I am adding my own answer based on the commenter s and my experience. Right now, there is no tool available. labor work is inevitable.