Although we haven't adopted yet, I have done some thinking about names (I've alluded to it before, but can't be bothered finding relevant posts, as I don't think I've written a whole post on this); I thought I'd weigh in on the debate, despite not being formally part of OA Roundtable.
UK social workers dealing with domestic adoption from foster care are very, very anti changing a child's birth name under almost any circumstances. Even where a child was abandoned in the hospital I have heard social workers say "but the nurses gave him the name". If a child's birth father and grandfather are both called Murgatroyd and they gave the son the name and, clearly, there are no other Murgatroyds in the country, it may not be safe for him to keep the name - most social workers would be positive about a name change under those circumstances. Otherwise not. I have also heard social workers saying that children must keep their original name's spelling, and their original nicknames (sometimes even if the nickname was given by a foster carer, not the birth parent).
They are very fixated on no name change. They "allow" addition of middle names, obviously change of last names (though recently the law has changed to allow no change of last name until the adoption is final; again I think safety may allow for exceptions). Until the adoption is final, the social workers are in your face, wherever you adopt. So, it's not a case of "my family, my rules". You'd be hard pressed to change a child's name when they had already been with you a year, although I know people who have fought for the right to change the name/spelling/nickname.
It sounds quite prejudiced - I think it is a social worker culture sort of thing, but also stemming from some of the Bad Old Days mistakes, ideas that children can just forget everything that happened before adoption, that it is best to pretend they are birth children.
I think I'd probably considered using a family name/name we had chosen for a middle name and, gradually if we/the child wanted, merging/changing over. For example, we saw a child in a Waiting Children newsletter with a name for which a nickname could be a shortened form of my mother's name, which I would like as a child's name. In this circumstance, we could keep the long version as a full name/first name but (even if the social workers said no, as it's something you can move into on a variable basis with a child) use the shortened form within the family. But if we were matched with siblings called Chardonnay and Wayne, I'm not sure what we would have done. Perhaps, as a forum contributor I read once said, have the best behaved Chardonnay and Wayne in the whole education system.
I don't know what UK social workers say about name changes for children adopted past babyhood from overseas; I would suspect it's the same, but from most countries adoptions are completed overseas so the social worker does not come along and "advise" post-placement.
When we decided that we might go for US infant adoption, one of the gifts I felt I had been given was the fact that I might get to give our child a family name. But now, reading some (sorry, especially US) comments on the whole name issue, I'm not so sure.
I'm not comfortable with the "did you give the birth family a say" question - perhaps it would be more honest to say to a child when they are older "your name before was X and your name now is Y"; acknowledging that the birth family did name them (if they did).
I think I'm of the opinion that, if a child is old enough to know their own name, then any changes should be minimal (or security-driven). I don't think you should take in an 8 year old and say "would you like to be called Charlotte now?" But parents shorten their children's names all the time (and children come home and say "I'm going to be called Aurora now").
I am also slightly agnostic about changes of names for children from overseas. On the one hand, children have names that are completely unpronounceable, or mean something strange in English (I understand that Nastia is a common shortening of Anastasia. Or perhaps it's for Natasha. Anyway).
On the other hand, the most common - and to me, cringeworthy - analogy is "We have a Polish builder, he just calls himself Paul, because it's the "same" as Pavel, he doesn't mind when people change his name". He's an adult. And his name is perfectly pronounceable in English.
So, look back here when we have been matched with a mixed-race, half African American baby whose mother has named him DuKwon.