gistfile1.clj

(defn map-and-update-in [m [k & ks] f]
  (let [value (k m)]
    (assoc m k (if ks
                 (if (map? value)
                   (map-and-update-in value (seq ks) f)
                   (map #(map-and-update-in % (seq ks) f) value))
                 (f value)))))

user> (map-and-update-in {:foos [{:bar {:bizzes [{:bam 3} {:bam 53}] }}
                                 {:bar {:bizzes [{:bam 5} {:bam 75}] }}]}
                         [:foos :bar :bizzes :bam] inc)
{:foos ({:bar {:bizzes ({:bam 4} {:bam 54})}} {:bar {:bizzes ({:bam 6} {:bam 76})}})}