Hey there,
Is it safe? Yes, for the most part. The monitor won't explode or anything

In terms of lifespan of the monitor. Yes, certainly OC'ing it can reduce that. But not like you might think. Let's say hypothetically it might last 5 years without any OC'ing, Well, then it might last only 4-4.5 yrs with the OC.
I've one of my monitors (BenQ 24inch) running at 75hz for last 3 years without issue. Even just the 15hz increase makes a difference, in onscreen smoothness. So for me It's defo worth it. With similar or better panels now going for 100£$€ it's a bit of a no brainer to try the OC and enjoy the extra FPS (actual) displaying on screen. Then if it goes in a few years, you can replace it with very little cost.