It appears Halo 5: Guardians will have slightly less customization options than in Halo Reach.
Halo 5: Guardians head, Josh Holmes, talked more about the customization options in the Team Beyond forums. Paradiger compiled his responses explaining the options you have in the new game.
First of all, Holmes confirmed there will be more customization options in the final game as compared to the beta. However, he said “the armor specifically is tied to helmets and suits” only. You cannot alter the “bits and bobs” like in Halo Reach.
Holmes defended this move saying 343 Industries designed a huge variety of suits in Halo 5: Guardians. There will be new designs as well as classic ones too. Armor options will also be unlocked through the game’s new REQ system. There will also be armor released via DLC too.
He also said why 343 Industries isn’t supporting interchangeable parts in the game such as different “helmet accessories and interchangeable shoulders, forearms, etc“. He said they were discarded because they didn’t have the “breadth and diversity of high quality content” the team wanted to support.
Customizing Spartans is cool, but it’s sad it will be somewhat limited in Halo 5: Guardians. Hopefully the designs are cool enough to satisfy everyone since they are aiming for “high quality” content throughout.