Underneath your tree of stuff, you'll see a tiny little button labeled "filter". Click on that, click on show library elements. Go to the very top of the tree of stuff and find the "commands" and "verbs" sections. In grey, you'll see a bunch of built-in verb responses. Find the ones you want to change, click them, click copy and you will be able to edit them. For commands, just delete this,
msg (Template("DefaultHelp"))
for example under "help" and add your own script. For verbs, make sure you change the default type from 'template' to either text or expression (whichever type of code you want to run). Should work. I just got done changing a bunch of my own! =)
You may, however, want to make a universal command for some of your verbs/commands, like the listen. You could do this for your command if you want all "listen to [object]" to have the same output. Add command. Type listen to #text# and add a print msg script like, 'You listen to that, but you hear nothing' or you can print msg 'I don't understand your command.', but that, to me personally, doesn't make sense. You could also type listen to #object# and the default for a matched object would be whatever you want to change it to, or in the event of an unmatched object, I think it will print "I can't see that." (or something like that).