Hi, I'm usually comfortable with truss-rod adjustments. But this sounds like one I'd be taking to a tech.
Why did the tech have to heat treat it? Was he not able to unfreeze the screw either? The first thing I'd want to do is get the screw freed up so it can do its job properly. I've seen a video about fixing that, not sure where, might be on stewmac. Thankfully I've never had to do it, though. It's pretty much get the nut/screw off without stripping it, cleaning it up, making sure it moves smoothly, then putting it back on.
When the screw is working smoothly, yes, I've also heard that you can coax a neck into straightening by loosening the rod, holding the neck straight and then tightening the rod back up. I can't remember whether you do this with strings on or not... Also very extreme cases involve heat/steam, I think. I'm pretty certain though, all of these things rely on the fact that the truss rod is capable of being adjusted. If the screw is frozen or hasn't got enough of an adjustable range, it can't do the job...
That's about the extent of my knowledge, and I have to admit that if I couldn't move the screw (even to loosen it), or if I could but the tightest I'm prepared to take it still results in too much relief, then I'd be taking it to a tech myself. I'd like to be able to watch and learn, but there's so much expensive damage I could do with the knowledge/experience I have at the moment.
I think, if it was so bad that the only option was replacing the entire truss-rod, then replacing the entire neck would probably be cheaper. I'd have to really love the neck to have it taken to pieces and rebuilt.
:( Good luck