No doubt, although I'd guess that repeatedly doing it would lower the chances to zero of successfully remaking the join before it killed the chip. Certainly, the more I did it, the more temporary it seemed to get.if you have to do this repeatedly you WILL shorten the chip lifespan.
I've written this machine off anyway, I no longer trust it enough to invest any more money in it so modded it last week. If and when it either dies or I find a game worth resubscribing to Live for, I'll just buy a new console, I don't think the new ones are subject to the same design and manufacturing flaws as my release model.
I can't help thinking that if this is a common problem which is known to be caused by a manufacturing defect then you have a claim under the Sale of Goods act, fitness for purpose etc.
Unfortunately mine died outside of the 3 year warranty meaning I didn't have a claim against MS directly and it wasn't worth claiming on the house insurance for £100 or whatever it's worth now.
Anyway, I fancied opening it up and having a go at fixing it as I was no longer buying games for it at that point. SWMBO wanted it as a media extender for the bedroom which I hoped would be a light enough load that the machine wouldn't keep failing, but that wasn't the case unfortunately.
My soldering is a bit rusty these days but circuit board repairs used to be part of my job. If you have a dry joint then it needs to be resoldered, as in remove the old solder and replace with fresh. Flux is to help create the bond and needs to be in contact with the surfaces to be joined, if you don't remove the old solder first then the flux may not reach the right places and you'll get another dry joint. If all the flux burns off during soldering there's nothing wrong as long as a good joint has been made with enough heat.
What you are doing sounds like a poor bodge, probably the best available because it's impractical to do it properly but is still likely to fail.
Still worth a try though.
I'm not even sure you'd need to replace the x-clamps, I'd just reflux the GPU to start with. Of course, since the x-clamp would need to come off in order to remove the GPU's heat sink, you might as well replace it with bolts.