Normally this is taken care of using a "Is[FieldName]ReadOnly" or a converter. Unfortunately I don't know what the reasons are why a field must be enabled/disabled, so I cannot give you a complete answer. In Catel there are some generic ways to check security and enable/disable controls based on the results.
What you can do is to create a generic IAuthenticationProvider as explained here to enable/disable fields in a generic way (for example, based on roles, or if models are read-only, or whatever you like).
You can also check out the tons of converters that ship with Catel.