Can I change the date format without touch the code level? I only have admin access. Tried to search for solution but all of them are code level.
If you are asking, can you change the Authored on/create time when adding or editing a node, eg, here:
then no, there isn't a way to do it without going in and doing a
form_alter() or similar.
However, if you mean the submitted date shown on the node, eg, here:
then yes, you can, as it uses the
medium format and you have some limited options available at
admin/config/regional/date-time. So, you can change, for example,
but just realize that every place that Drupal uses the medium date format will now use this new one as well.
Yes you can. As an admin you can access "Administration xc2xbb Configuration xc2xbb Regional and language xc2xbb Date and time", where you can define date formats and and display types. The latter you can then use in the "Manage display" part of an entities field configuration, or in the view display options of date fields.
Edit: If that doesn't work (which it doesn't for default node displays) and adding preprocess code is not an option (as the OP declares), another option is to hide the "created by" output (content type settings) and adding an own date field that you can fully control. This one will not, out of itself, be set to the current date when creating a node. Though, that might be an option in the field settings, have to look.
Anyway, code level change would be trivial, but without touching code, this is one of those Drupal WTF moments.