No you cannot change after channel open. It has to be set at the time of opening.
Noob question…can you change a #lightning channel type from private to public? Trying to attach my node to nostr:npub19tcpurtt6xulhw0r6sc404j9jraj0h8me2lzs7z2tqewz7l0hpas59nlea but it’s saying it needs to see at least one channel on the graph first and both channels on that node are private. That’s the only thing I think I’ve done different between my two nodes.