...snip...
I think in this case it would be ok to update.
In the strict sense this could cause some EPEL users to be broken, so
it's bad, but I think it would be a very small % of users, and the rest
of the update is worth that small amount of pain.
I don't think very many people do custom tools against the bzr api, and
if they do they should be in reasonable shape to build against the
newer one since everything else is already using it.
So, I would say announce loudly and go ahead.
kevin