If Neo Deadly Rave is made unblockable by the attack's static text, if Terry's First E is used, is the attack blockable again or does it stay unblockable?

No, it's still unblockable. Terry prevents attacks from being made unblockable, but Neo Deadly Rave has already been made unblockable.

Neo Deadly Rave if it qualifies for it's unblockable text, is already unblockable prior to the E being added to it.

So, yes, Terry can make it an unblockable big beefy attack.

*Drats! Ninja'd by Tag!*