Be careful while renaming a security policy on JunOS, since it will close the current session.
Unfortunately, what JunOS does, is removing the old-named policy and adds a new one.
I tried also with adding a new policy, inserting it before the old one, commit, then removing the old one and commit. But again interruption, which logically makes sense.
Test environment: JunOS 12.1X44-D35.5 on a SRX240h
I tried on vsrx firefly-perimeter with JunOS 12.1X47-D20.7 and faced no drop!