I've been slowly turning on more iCloud services, but am in a weird state where my media and purchases use my "preferred" iCloud account ([email protected]), while all of the other native iCloud services use my [email protected] account... which I can't figure out how to change to [email protected].
I'm surprised there aren't more people who are in this situation. I got into this mess because Mobile Me required me to have a different account than my iTunes account ([email protected]), and then that eventually became iCloud, while app purchases and everything else stayed with my iTunes account.
I'd love to merge them, and I have absolutely no idea how to. I don't even think this guide that you linked to helps me much, to be honest. I'd be too afraid to lose something.
Your mission, should you choose to accept it, is find the support engineer who knows that.
I have two Apple IDs and I'd desperately love to merge them.
https://www.brianstucki.com/blog/how-to-manually-merge-two-a...
I don't know how many folks are in this situation, but obviously not enough for Apple to care about offering a solution.