I think that’s a misunderstanding. The CLI commands are not intended to configure a running instance. Instead, you can use dropbear -w to start a new instance in addition. Normally, this doesn’t work because port 22 is already occupied by the active SSH server.
Take a look at your log after you’ve executed dropbear -w. You should find the following there:
Aug 10 10:24:09 DietPiZ2 dropbear[6989]: Failed listening on '22': Error listening: Address already in use
Aug 10 10:24:09 DietPiZ2 dropbear[6989]: Early exit: No listening ports available.
For a permanent change, the configuration file must be used.