transition permission cannot depend based on the attribute.
Need a PlugIn for this condition.

Easier way is to make the Requirement Defect as a separate work item type. Or do not control the defect workflow role based, except few states.

There are permissions that control which role is allowed to create or save specific work item types, so you can control this. If you need to get more complex, there would be additional options.

Personally I think that the bigger problem of a lot of users of tools like RTC is that they have a culture of distrust and try to gouvern the process to an extent where it gets into the way of a usual usage. So I think it is more disrupting to try for a tight control to compensate for team trust and enablement. It is better to advise users in case of errors and that makes a process way better over time as well, compared to trying to keep tight control.

About Roles in RTC.

In RTC a user has at least one role (everyone/default) and can have multiple roles.
Assigning roles to a user is an administrative task that requires certain permissions and actually requires to save the process specification. This is definitely not anything that you want to dynamically do in any automation. Dependent on the approach this automation would run in the context of the current user and thus would require all users to have permission to save the process. This is pretty much the admins nightmare. You definitely don't want to go into this direction.

Important reading:

Process behavior lookup in Rational Team Concert 2.0


Custom operation behavior:

It is possible to write so called pre conditions (advisors) for RTC that can check certain situations and prevent saving. See https://rsjazz.wordpress.com/2015/09/30/learning-to-fly-getting-started-with-the-rtc-java-apis/ to find out how you can do that.