Not me, but my wife's family held on to a big secret for years, and it only came out a few years ago. Basically, my wife's grandmother and her children assumed the identity of another family that died in the Blitz on London in the early years of WW2. The children of the dead family were slightly older than those of my wife's family and they had a house, so the wife's grandma told everyone that she and her children were the other family, and tried to get better accommodation from the authorities.
I've no idea whether it worked or not, because my mother-in-law wouldn't talk about it when she was alive. But after she died my wife did some digging and found out the truth. She then confronted her living aunts and uncles about it and they admitted it. That was why her uncle Eddy was really uncle John. Several other of the children (there were 5 altogether) also had two names, one of which was their proper name and the other of which was the name they assumed.
The only secret my mum ever kept from me was that I was born the wrong side of the blanket. She told me my dad was a soldier and posted overseas. However, as I got older she gave up the pretense and told me the truth, that I was the product of a date rape. It hasn't affected me all that much except for the lack of money when I was young, as we didn't have the income of a father to keep the family finances afloat.