As a part of a photo-backup solution, I suggested my daughter get her own Flickr account. Then something went terribly wrong. I call it, "Yahoo!"
I was thrilled to find they had a, "Sign in with Google" button because she already has a Google account. However, it was a feint - "This Google account is not linked with your Yahoo! ID." So not really.
I had to create her a Yahoo! ID. Thankfully, they allow younger than 13-year olds their own "login ID" (which may or may not be different than their own account) with the permission of a parent. I paid $.50 to prove I was an adult (or at least someone with a credit card which is silly since my 12-year old daughter has her own debit card and could presumably "prove" she was her own adult? And "a portion" of which goes to charity? That verbiage makes me awfully suspicious - as if only %0.001 were to actually reach its destination) Much like I've linked my defunct Yahoo! ID to my Google e-mail as a backup account, I also linked her new Yahoo! ID to my Google e-mail as backup.
So now Flickr returns, "THERE IS ALREADY AN ACCOUNT WITH THIS EMAIL ADDRESS!" Not her new Yahoo! email address, her new Yahoo! email address' linked parental account <-- My Flickr account. SHE CANNOT CREATE A FLICKR ACCOUNT WITH A YAHOO! ID. Which was of course my understanding. Wasn't it yours?
I wish this was where the asininity ended, because like me, you're thinking I could just go back into her account and change her backup email from my Google email to my Yahoo ID account. Only...that option is not available - presumably because she's a sub-account to my own. No problem, right? Just go into my own Yahoo! account and change it there.
THERE ARE NO OPTIONS FOR THAT.