I was specifically thinking of the change in title in the mid 1700's for Prussia. (Kingdom in/kingdom of), but i would also be curious to know if this distinction was unique to them or if other political areas also had a similar transition in name/form.
Mentioning previous replies is not intended to discourage follow-on questions, info, and debate.
Especially in this case, because these deal with "king in Prussia", although some compare it with kingdoms of Bohemia, Poland, Germany, et cetera -- not the possible existence of any other "king in" titles.
"When, how, and why did Brandenburg change to Prussia?" at https://www.reddit.com/r/AskHistorians/comments/5y3mxx/when_how_and_why_did_brandenburg_change_to_prussia/den6xk8/ , a reply by /u/kieslowskifan
"Why did it take so long for the various German States to unify into one nation?" , a subreply at https://www.reddit.com/r/AskHistorians/comments/6rheh5/why_did_it_take_so_long_for_the_various_german/dl6yexr/ by /u/LiterallyBismarck
"Within the Holy Roman Empire, why were the Hohenzollerns forced to use the title "King in Prussia" while the Wettins were referred to as "King of Poland"?" at https://www.reddit.com/r/AskHistorians/comments/7uq9q7/within_the_holy_roman_empire_why_were_the/ , with discussion by /u/coldsteeleyes , captkrob, Erusian, laertes78, and iwanttosaysmth.