This line in rpm-spec-mode.el:

  (define-key rpm-spec-mode-map "\C-u\C-c\C-i" 'rpm-change-tag)

Makes C-u stop working properly as a universal argument when editing spec
files.  This is now what you need to do here.  What you need to do here is
something like this:

--- rpm-spec-mode.el	2001/06/03 06:30:17	1.1
+++ rpm-spec-mode.el	2001/06/03 06:29:47
@@ -325,7 +325,6 @@
   (define-key rpm-spec-mode-map "\C-cxt" 'rpm-toggle-test)
   ;;May be better to have movement commands on \C-ck, and build on
\C-c\C-k
   (define-key rpm-spec-mode-map "\C-c\C-i" 'rpm-insert-tag)
-  (define-key rpm-spec-mode-map "\C-u\C-c\C-i" 'rpm-change-tag)
   (define-key rpm-spec-mode-map "\C-c\C-n" 'rpm-forward-section)
   (define-key rpm-spec-mode-map "\C-c\C-p" 'rpm-backward-section)
   (define-key rpm-spec-mode-map "\C-c\C-t" 'rpm-insert-true-prefix)
@@ -659,9 +658,11 @@
       (message "Group tag not found..."))))
 
 (defun rpm-insert-tag (&optional arg)
-  "Insert a tag."
+  "Insert or change a tag."
   (interactive "p")
-  (rpm-insert))
+  (if current-prefix-arg
+      (rpm-change)
+    (rpm-insert)))
 
 (defun rpm-change-tag (&optional arg)
   "Change a tag."