Attention to everyone who can NOT pick a new specilisation when they are rank 80+. I have a solution to the problem. It as worked for me twice.
What you’ll need is a USB:
Put your USB into your console before you start Halo 4!
When the main menu is open press start as always and it will say select hardrive, select your consoles hard drive!
Then check if specilisations are there or not, if still not there, take your USB out while you are still in the specilisation options.
This will ask you to select your hard drive again, select your consoles hard drive again and they SHOULD be there.
It worked for me and I hope it works for you people who’s ranks are stuck. Good Luck!