Promising and Autonomy

In the Genealogy of Morals, II, 2, Nietzsche classifies Promising as an 'autonomous' act, and then proceeds to classify Autonomy as 'supramoral', in apparent defiance of the Kantian doctrine that equates Morality and Autonomy.  However, this challenge to Kant is undermined by a vacillation in his own rhetoric.  For, in this passage, 'morality' clearly means 'morality of custom', an alternative to which he recognizes, in Daybreak 9, as a "morality of self-control".  In other words, if he is repudiating Kant in GM, then he is also repudiating his own earlier position, without explanation.  But, what likely amounts to no more than a terminological inconsistency distracts from the sharper distinction from Kant's doctrine that Nietzsche is at least implicitly drawing.  That is, for Kant, the involvement of Autonomy in Promising is only in the case in which the temptation to make a false promise is resisted, as a result of deliberate application of the principle of Pure Practical Reason to the maxim formulating the intention.  In other words, Promising is, itself, not an autonomous act, as it is for Nietzsche.  So, what Nietzsche is actually exposing in Kant's concept of Autonomy is its inherent and restrictive negativity, i. e. that it is a power of constraint, but not of creativity.