Well, in the DBNPC you can store the classes object. And manipulate it from there...
Like, in the class, you could have.
PHP Code:
function onCreated()
findNPC("npc_name").testvariable = this;
and in the dbnpc have
PHP Code:
function onManipulateClass()
{
with(this.testvariable)
this.chat = "[test]";
}