Forgive me if I’m missing something obvious, but why are you renumbering at all?
Of course the diversification of RIRs is a good thing, but couldn’t that be accomplished just as well by transferring the current allocation to LACNIC?
It seems to me that there are a lot of reasons why, when it concerns root servers, renumbering should be a last resort. Especially when you already renumbered relatively recently and when an administrative solution rather than an operational one is available.
I administer a few public IRC servers for EFnet, and when I assign a /24 for such a server I consider the subnet unfit for any other purpose from that point forward. Practically lost for normal use.
Now, a DNS root server is obviously not the same as an IRC server, but I’d guess that there is a lot in common concerning threats and mitigation of those threats. Only the scale is much larger and the service (much) more critical (though people on IRC will fight me for saying that :).
So, it seems to me that you’d also like to avoid renumbering unless absolutely necessary, if only because it’s a waste of a perfectly good subnet.
NB. Apologies for top-posting, a script that is supposed to fix this is started corrupting my emails after an update and I haven’t been able to find the problem.