The coronation is months away, he was protesting the ascension at the Queen's funeral procession. That does not avoid disparagement of the Queen.
I certainly don't think he should be arrested but he's clearly boneheaded. He'll have plenty of time to protest both the ascension and the coronation, of someone who is a much softer target that the Queen, especially considering she's just died.
PR own goal if ever there was one. Even Extinction Rebellion have had the good sense to postpone their demos. Is there anyone but the Western Baptist Church who thinks it's a good idea to protest at funerals?
They say if you support free speech you'll end up defending vile people, and it's true, he shouldn't be arrested, he should be allowed to say what he said, but he is vile and it was stupid.
Symon Hill was arrested for protesting at the regional proclamation in Oxford: https://www.oxfordmail.co.uk/news/21275817.photo-gallery-pro...
Where did you get the impression that this was a funeral procession?
Which means it was still not a coronation, it also wasn't a funeral procession, I still think he's boneheaded but not as much as before or nearly as much as the ones in Edinburgh, and none of them should've been arrested (maybe perhaps the one that shouted at Prince Andrew, but definitely not the others).
If that falls under the rule you're describing, doesn't that render it impossible to protest a ceremony, as long as it happens after a funeral? It seems you're defining away the protest of hereditary succession as unacceptably rude?