Rick ChurchillMy phone was playing up when I changed my Apple ID. It was asking me to sign into the previous Apple ID even though in Settings it was showing the new ID under my name and also in "iTunes & App Stores". After an hour with one Apple man then, when he couldn't solve it, with an Apple man from Portugal the only way out was to reset the phone. This is more trouble than it sounds.
So before changing your Apple ID on the Mac, especially from a 3rd Party email address (like talktalk) where there is no way to go back now Apple do not allow 3rd Party addresses, make sure that the phone and iPad are both signed out of ALL iCloud services. The one I left was Find My Phone/iPad.
Else your phone/iPad will nag you to sign into the previous ID account which no longer exists! Had Apple allowed me I could have altered it back and closed all the services down.