Re: Sign in screen on my Iphone 5s has made it almost unusable
Wipe the iPhone? Yes you can do that, but while reinstalling the system, but the time installation configuration will reach 98%, apple will ask you for the previously "find my phone" user name and password. Until you will enter those credentials, your iPhone will be as good as a brick.
I may be wrong but your story actually seems not straight.
Say your email is firstname.lastname@example.org and the password is user123, your iCloud credentials can have the user name email@example.com but will not have that password user123. Instead it will be another password dedicated to iCloud only.
This said, you can change your non iCloud email account password without affecting your iCloud account password (does that make sense?)
You may forget your email password, but you didn't forget the password you've used on your iCloud because you didn't change that iCloud password. So just type in your iCloud or iTunes, or apps store password that is related to your email address and it should work.
I have a hotmail account with its own password. I use my hotmail ID for my iTunes, iCloud, apps store accounts but with another password different from the one I use for hotmail. Should I have any issue with my hotmail account password, my iCloud, iTunes, apps store will not really be affected.
Unless my drive mail account is iCloud.com which I use for my iTunes, iCloud, apps store, if I change the password of that iCloud mail account then it populate the password changes in the other iTunes, iCloud, apps store services as well. In that case, that pop up notification will appear asking me to enter password. And if you don't know what it is, then go to Apple Store with the iPhone ownership receipt in order to have it reset and unlocked.
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