Hi,
If you need to have this field editable for some user groups, you can do as follows in the version below 16.0
* in the original view, set the readonly attribute for the field based on the state
* Once this is done, field will be readonly in the state and create wont be visible
* now create an inherited view, and set the user group(for need to be editable always) for this view
* remove readonly attribute for the field from here
By doing this, for normal users the create wont be visible always and for higher group, always it can be edited.
You can see more here: Apply Changes In A View For Particular User Groups In Odoo
Thanks