Changing permalink name into a category

Hi,
When I set my website, I made the mistake of setting up the custom permalink structure like this:

Website.com/diary/%category%/%postname%/

My URLs currently read like this for the category “Asia” and subcategory “India”:

Website.com/diary/asia/india/postname

But what I should have done and what I like to achieve now, is turning “diary” into the main category, so that I can filter everything belonging into a diary category and setup categories that are entirely different. But the change would need to be done without changing the URL and without losing the social connection, comments, likes and so forth.
So if I take “diary” out of the custom permalink:

Website.com/%category%/%postname%/

Does WordPress automatically change all my URLs?
And if I then create a new category called “diary” while making “Asia” the sub-category and “India” the sub-sub-category, would the final URL be the same as it was in the beginning?

Is that change possible without screwing up anything and keeping all the connections, links, comments and likes?

Thank a lot for your help!
Dennis