I have a character vector

xx <- c ("AB", "BA", "CA")

I would like to insert the word “hello” after the first element, but only if this element is not A. I would like to get: “AB”, “BhelloA”, “ChelloA”

I have figured out how to reference the desired pattern after which I want the insertion: “(?=^)[^A]”. But how do I instruct R (preferably in stringr package to insert the desired pattern)?