nostr-rs-relay

If you haven’t been following along, I have a couple of nostr posts at this point. https://nessy.info/tags/nostr/ I’ve been trying to further understand nostr by deep diving the protocol. At this point my thought is how mutable are nostr messages (events), I understand that during broadcast the relay verifies the signature, but then they need to store these events in some centralized database, right? Could a rogue relay for example accept your event, then alter it at a later time?