If you can change the thermal paste without damaging anything (not even scratching!) then I don't think that anyone would realize that you've take it apart... officially it would void the warranty, of course...

Same with the VBIOS... save the original one, but if you can flash it without bricking the card (a wrong VBIOS can render your card completely useless), then you're good to go...

Both things are doable, but if you never done them, do your homework before you start!