We have an older v6.5 ESXi host that needs to be updated. Unfortunately, it's on an older build whose VIB Certificate is now expired. KB article 76555 details the issue, but doesn't list any solutions. The workaround merely says to upgrade before the cert expires, which is of course no longer possible. I haven't attempted the update yet, but I'm expecting it to fail based on what the KB article is saying.
Is there a way to upgrade the ESXi build on this host without fiddling with the system clock?
From which version 6.5 Build ? you are trying to upgrade to which Build version.
You must validate that your server and/or hardware is compatible with the version you are upgrading to
So you are on ESXi650-201710001 (6765664), I recommend you to upgrade to Update 3 (build 13932383) first.
The latest level is ESXi650-202102001 (Build 17477841)
you need a user and password, you can register for free