Hey @Jeremy, glad to hear you like my plugins 
As for your question: I don’t have much experience with Buttons, but I tried my hand at making it work. From what I could tell, you’d want to either make it insert a Templater template into the file, where the template contains an API call to MetaEdit’s update.
You could also just make the button call a QuickAdd capture/macro, which could also call the update function.