draft-ietf-smime-esformats Commitment Indication Type Attribute

In this draft we have the Commitment Indication Type Attribute indicating a
type of commitment to the message. We have a generic type proofOfApproval.
But in some cases I would not approve the message and tell it to the other
party. But there is no generic type to indicate that. 
Is there a way to add this as a new generic commitment type?

Bernd