Here's a story from Cat about how not to re-boil an egg if your hardboiled egg comes out runny.
"So, a couple evenings ago I decided I wanted to make some egg salad for a sandwich to take to work for lunch the next day. I put the eggs on the stove to boil, then went to go fold some laundry. I came back and saw that the water was already boiling. I didn't want the eggs to be overdone, so I immediately took them off the burner. Unfortunately, they must not have been boiling enough, because when I peeled them, the yolks were still gooey inside. Oops.
I grabbed a microwave safe bowl, filled it with water and popped the eggs in, then stuck them in the microwave for two minutes. I have a lot of friends who hard boil eggs in the microwave, so I didn't think anything of it. Well, the beeping goes off, so I reach in and carefully pick up the eggs....
BOOM! The eggs EXPLODE everywhere! Boiling water flung all over my face. My boyfriend was immediately there. After I ran to the bathroom and washed out my eyes, he helped me clean up the mess. Getting egg off the CEILING sucks. I held a box of frozen vegetables against my face for a while and soon the ouchies stopped...so yeah...all good. And lesson learned. And now I have post-traumatic stress disorder from hard boiled eggs."