[O] Rescheduling timestamps on a headline (not the next line)

[Michael Hoffman]

I am using org-mode 8.2.10. I often like to keep SCHEDULED and DEADLINE 
timestamps on the headline so they are more compact and show up even 
when I have collapsed that tree. Unfortunately, in this case, 
(org-schedule) and (org-deadline) add a new timestamp on the second line 
instead of replacing the previous schedule.

Steps to reproduce:
1. Visit new file `test.org`
2. Enter `* Task SCHEDULED: <2015-09-19>` in the buffer
3. C-c C-s for (org-schedule)
4. S-right to select 2015-09-20
5. RET

Output:

* Task SCHEDULED: <2015-09-19>
  SCHEDULED: <2015-09-20 Sun>

What I expected:

* Task SCHEDULED: <2015-09-20 Sun>

Is there a way to get my expected output? (org-add-planning-info) seems 
to go to the end of the headline:

            (org-back-to-heading t)
            (looking-at (concat org-outline-regexp "\\( *\\)[^\r\n]*"))
            (goto-char (match-end 1))
            (setq col (current-column))
            (goto-char (match-end 0))

Before it starts looking for text to replace.

Many thanks,
Michael