You can update your welcome guide on THS and it will automatically let the sitter know that it’s been updated — the sitter gets automatic notification from THS. No need to reshare. At least that’s how I’ve experienced it as a sitter.
It’s annoying if the guide is updated multiple times, because THS doesn’t indicate where the changes are, so you have to read the whole guide over to avoid missing anything, especially theoretically in case you end up with a creepy host who tries to hide info.