True, I also want to be able to change the original published date. I requested the same thing in november 2016 (see; Change "created on" date manually (CMS)) - But still nothing 
But using a manual published field will work as well. I do it like this as well for clients who want to add older posts.
Then in the designer you can use seperate text blocks to grab the date, month and year seperately. That way you can use different date structures.
See image attached. Here I used 3 different text blocks to create the date format I want.
