Change over all date format


I can change over all date format from system settings doc. But the date format I want is not there in list i.e. dd-mmm-yyyy.
How can I have this?
Even If I manually add this format in system setting doctype in “Date Format” field option value, and select that date format in system settings doc. It throws error. So, I guess frappe is not supporting this format.
So, Is it possible to have this format?