Were children often renamed in late Saxon England?

Baptism is one time only in a life in the Roman Catholic Church.

So this fiction has a major research fail: an Anglo-Saxon (AS) Christian will be Roman Catholic Church, not Protestant anabaptist religion, and cannot be re-baptised. At confirmation, in modern usage he may add a favorite saint's name to his own and take up using it, but that's modern. Camden remarks on it being unusual in his time. Time of the novel, AS never took confirmation names, so there is no mechanism for him adding or changing his name, other than just loosely using a nickname. It is never official.

Also, since the AS only used one name, no surnames, only patronymics, they never named children after their fathers. They would riff on a name element (how many ways can you use Aethel?) but they would avoid repeating them in memory.

If you go through the AS Chronicle for names, you find very few repeats before 1000, as opposed to that of, say, Norman times.

However, many people would change their names if their circumstances changed or they moved. Also, people would adopt names to disguise their identity especially if they were engaged in warfare or banditry. Sometimes people would adopt a special name just for the purpose of traveling, especially if their regular name was unsuitable in place they might be traveling through for some reason. If a person changed social status or stature, their name could change.

I have never seen evidence that AS did change their names on moving somewhere else. I think you are referring to locative bynames/surnames of a Norman England. I have not seen any mention of noms de guerre.

Banditry, yeah, people take nicknames, but they're social outlaws.

AS did not change names with changing social status: it's fixed by the Church baptism. This is because names had no status: it's not like on the Continent where a Frankish or Latin name might be perceived as higher status, or where your Christianized viking has to become Rollo in place of Rolf to Frankify him.

You are probably misunderstanding "Early Medieval," probably continuing into 1200s and Continental practices, as opposed to purely Anglo-Saxon English only.

For example, St. Patrick went through 3 or 4 names during his life. Some people, especially clergy, might have two different names: one for local purposes, and another one, in Latin for clerical purposes.

St. Patrick was Roman Briton of the 5th C, not a 9th C Anglo-Saxon. Also, I find reliably only a birth name and a post-ordination name, not 3 or 4. Those are later synonyms, like titles, if you mean the list "Magonus, Succetus, Patricius, Cothirtiacus." (The last would be a 5th C Irish pronunciation of Patricius.)

AS did not have another name for clerical purposes: the clerk just wrote down a Latin version of their one and only AS name. Some priests chose to adopt new names on going into the Church, but it's rare and mostly a Continental habit, like Maewyn did becoming Patricius -- in France.

SOURCES:

Redin, Mats. Studies on Uncompounded Personal Names in Old English; in Uppsala Universitets Arsskrift

Searle, William George. Onomasticon Anglo-Saxonicum. A List of Anglo-Saxon Proper Names from the Time of Beda to that of King John

Seibs, Benno. Die personnennamen der germanen

Kelham, Robert. Domesday Book Illustrated: Containing an Account of the Antient Record; as Also, of the Tenants in Capite or Serjanty therein mentions: and a Translation of the difficult passages, with occasional Notes; An Explanation of the Terms, Abbreviations, and names of Foreign Abbies: and an Alphabetical Table of the Tenants &c.

Ingraham, Holly. People's Names

@lazarusL - Thank you for saving me from ever reading any of Cornwell's novels. Anyone who can't get a basic of Catholic practice right is going to have a lot of other annoying social anachronisms, even if he has the weaponry down perfectly. The stories may be "splendid" but his grasp of the social milieu is obviously poor. He should be setting these in a magic-free invented world.