Where to edit source

Ok, I need to edit the source for a port (tetex) to increase one of its arcane parameters. I'm struggling with how I extract the source, edit the file, and get port to build the new version. I suppose I could add a patch, but since this is just a local change for me, it seems like overkill. I have done 'port extract tetex' but it doesn't seem to do anything. Am I barking up the wrong tree? Thanks, ET