Sorry if this is a bit dim, but I've not been following the security hoo-ha terribly closely so not sure I have it right... My understanding is that Harry (and his US family) will remain eligible for security if it is deemed necessary. And as he is so very unpopular in the UK, I would guess it would be considered necessary if he ever chooses to grace us with his presence. I don't really see that Charles, or anyone else, wants him to be mobbed or attacked - imagine the headlines if he were!
So how are things different for him now? He just has to tell us he's coming and we'll have a set of scary bodyguards waiting to protect his life and limb as soon as he touches down. Is all this because he begrudges having to announce his plans in advance and instead expects the (taxpayer-funded) bodyguards to be sitting around 24/7 twiddling their thumbs, just in case he wants to pop over on a whim?