One thing that always used to wind me right up was the fact that once you hit save to create an entity in MSDYNCRM, you could not change any details about the primary attribute.
However, after a bit of searching i found this blog on the Microsoft Dynamics Community site that was very helpful.
Modifying properties of primary attribute is disabled when you try to do it from “Primary Attribute” tab. However you can change the properties if you opened the attribute from Attributes left navigation instead.
1. Go to Attributes and select “name” i.e. primary attribute of entity. As shown in below screen shot.
Brilliant eh?! Above you have seen how to change the requirement level but this obviously also applies to the display name of the entity. This is particularly handy if you are renaming entities.