In HMQV, can one use multiple identities with one public key?

The HMQV protocol has 2 "identity" fields $\hat{A}, \hat{B}$ that are used in the dual signature - and it tries to guarantee that any properly-generated session key is only shared by a single $(A, B, \hat{A}, \hat{B})$ 4-tuple.

However, the paper isn't particularly clear whether a party can use multiple, potentially attacker-controlled, identities.

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I think you have not familiar with the PKI-based setting, in the PKI-based setting, each user own a certificate that binds his/her identity with his/her public key. If a user uses multiple identities with one public key, that means he/she must use same public key with different identity to register many times, at this time he/she will receive different certificates(the number of which is the number of the identities belong to a user). Well, this occasion is very easy to avoid in the $\mathcal{CA}$, it just require that repeat register is unallowable.