I think that's a given. If you have a 3ghz processor and run it at lower voltage and 2ghz, it'll last longer. If you up the voltage and run it at 4ghz, it'll die sooner. If you run it at 3.2ghz and don't up the voltage, you're still going to kill it sooner. But in all those scenario's, how much of an effect each action has, is different.
So in short, yes. Running it at 100hz while it's intended to run at 60hz will kill it sooner. But probably not proportionally sooner. ie. Just because it's running 66% higher hz, doesn't mean a 5 year lifespan turns into a 3 year lifespan. It could turn it into a 4.5 year lifespan. Or...we never know...it could make it a 1 year lifespan. There are always risks and known reduced lifespan for all items we OC. I have a CPU that can't run on default bios settings anymore. It will only work if I up the voltage to it. Thanks to years of OC'ing. Video cards and CPU's see a quicker reduction in performance output over time as well, the more you OC them. But...this is overclock.net. We kinda like doing this sort of thing. And the risk involved is what makes it all so much fun. Because due to that risk, the majority of people won't do the same, and can't tout the same level of performance as we get from our gear. Even if our gear doesn't last as long.
To recap, yes. Shorter lifespan. No idea how much shorter. But regardless, well worth it. Can't beat an IPS 2560x1440 100hz display for $374 shipped...really...