In vim: :%s/\<div\>/p/g (add C at the end if you want to confirm each change)
Since the “word” in question is “<div>”, I thought the \< was just an escape. I looked in various docs and the best I see in Tcl re_syntax(n) is \< and \> are synonyms for [[:<:]] and [[:>:]] respectively, which are constraints matching empty strings at the beginning and end of words, where a word a sequence of word characters... [a-zA-Z0-9_]
TIL, too...