Our upgrade we did without removing any zenpacks. In fact, checking zenpacks.txt, I don't think the zenpack versions in the RPM changed from 4.2.3 to 4.2.4... I would never remove zenpacks "just because" that you plan to use after an upgrade, but do install updates first if possible to avoid potential breakage. I strongly believe in testing in case it all goes to hell.
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James Pulver
ZCA Member
CLASSE Computer Group
Cornell University