A premise can also be a subsidiary conclusion; however, for a premise to also be a subsidiary conclusion, there must be more than one premise in the stimulus.
In this example, the premise cannot also be a subsidiary conclusion because there is no additional premise to support it. The statement "bureaucratic mechanisms are engineered to resist change" is a fact that is used to support the conclusion that "it is unlikely that bureaucracies will be simplified."
Hope this helps! Please let us know if you have any further questions.