hi, i have recently bought an ibanez s470. it is my first proper trem fitted guitar. I am in the process of stretching the new set of strings i have fitted. My question is do i need to block off the trem while i do this?

also what is the purpose of the metal bar that covers the strings between the nut and the machine heads? in what way does this effect the string tension etc? I see these bars on a lot of ibanez guitars.

also does a double locking trem fitted guitar end up having more tension on a set of strings then say a fixed bridge guitar? it's just have 10-46 gauge on this guitar and they feel tighter than i am used too. the guitar is the same scale as my last guitar too.
The bar your talking about is what is known as a string retainer, it helps keep the action even throughout the course from the bridge to the machine head. As for the tension question, ensure that the trem is parallel to the body, oh and tuned correctly.