If you unpack the game's resources (see the wiki) you can use that as an example.

Netricsa messages are in gui/netricsa/data.sval, and can be given using the GiveNetricsaMessage worldscript.

Mission objectives I assume you mean waypoints. These can be set using the WaypointAdd worldscript, and unset using the WaypointRemove worldscript.

Are the netricsa mission texts in data.sval?

Yes, however in the main campaign they are localized, so you'll see strings starting with a period (.)

http://ssbd.a000ff.com/wiki/Netricsa_custom_objective

Thanks guys.