I'm utilising the underlying wysithtml5 libraries 'insertHTML' command on some custom buttons. To do this I've created a template that includes these commands and have added

custombuttons: true,

to my user options to get it to load. Only it doesn't load because the this library uses the defaultOptions to populate the toolbar and not the combined default/user options. To work around this I have added the above to the the underlying $.fn.wysihtml55.defaultOptions object. This realistically achieves the same but is not super intuitive.