(def ^{:key "val"} my-var "")
;;=> #'user/my-var
(meta #'my-var)
;;=> {:key "val", :ns #<Namespace user>, :name my-var, :file "NO_SOURCE_PATH", :column 1, :line 1}
(reset-meta! #'my-var {:new-key "new-val"}) ; replace all metadata
;;=> {:new-key "new-val"}
(meta #'my-var)
;;=> {:new-key "new-val"}