It’s bit odd to see Lilomar changing his mind and rescinding a veto, and it looks like some (but possibly not all) of the current ruleset wording supports that. But self-kills explicitly can’t be changed (“If a Citizen Votes against their own Proposal, that Vote may not be changed.”), and I’d say vetoes should be the same. They’re both one-shot “this proposal will now definitely fail”, which means we can stop voting and get on with reproposing or doing something else. If the Emperor vetoes a contentious proposal, we can stop discussing it, rather than continuing to debate and vote in case he’s won over before it gets processed.