Change primary apple icloud id
I have 2 icloud id's. I am trying to change my primary icloud id to the other one. I am unable to do so as if I sign out from the primary apple/icloud id, I am afraid all my data, photos, various apps etc will be logged out too. I just want to change/edit the primary apple/icloud id to another icloud id (analogous to editing a name/spelling). I want all the rest of the information to stay the same, only edit and change the icloud id associated with my iPhone.
I am also unable to add the other icloud email id to my mails (settings > mail > add account > icloud)