If Chef configuration was defined in the Role Scope, then you will only be able to edit Chef attributes (though, Global Variable Interpolation may have been used in the Role Scope to expose a certain level of configurability to you).
To edit Chef attributes, click "Override attributes defined on Role level"
If Chef Configuration was defined in the Role Scope, then you won't be able to edit anything in the Bootstrap with Chef Tab, except for Chef attributes and the Chef logging level.
As a general rule, we recommend using Global Variable Interpolation rather than overriding attributes.
Doing so ensures that future changes made in the Role Scope will be reflected in Farm Roles.
To override Chef attributes, click "Override attributes defined on Role level". Note that changes made in the Role scope will no longer be reflected in your Farm Role.