Which is why you getting a new identity is not going to work for the best at all.
[sigh]
If we accept that you're not Rory, then we'll have to accept to sacrifice a member of our family in order to get him back. And you, on the other hand, will keep comparing yourself to Rory and live with the knowledge that as things are right now, you are second-best.
If we neatly divide the two identities, then this is bound to end in tears no matter what. You're right in saying that as things are right now, Rory is the person Lyvus needs. But that doesn't necessarily mean "Brass" is not needed.
It may not look like it for you right now, since you remember him as a curse from the Gods... but you two are one and the same. Rory wouldn't be Rory if there wasn't some of you in him. So you're not... expendable.