I want to use custom post to build a global configuration for the site use, as this is global configuration, so there is only one post in this post-type. Is it possible to disallow the user to add new post to this post-type?
If I understand correctly you want to create a new post type but you don't want your users to be able to create posts under that post type ?
Are your users using custom roles ? Or do you have the access plugin installed?
Because you can just setup the permissions for the custom post types at Toolset -> Access Control , select manage with access then just uncheck the the publish permissions from the post type.
Do you want the post type to be visible to the other users ?
Yes, I only want editor role to update the post but not able to create, if I have several users are administrator role, can I disallow some of them to create also?
Unfortunately you won't be able to setup permissions like these for Admin roles, however you can for the editor role.
What you need to do is to Disable the Publish permissions but enable the Edit Any permission. Once this is enable the editors will be able to edit the posts but they can only save them as drafts.
