I tried another and this doesn't do it.
if(event.target.value == "Yes"){
this.getTemplate("Authorities4-6").spawn(event.target.page+1, true, false);
this.pageNum = event.target.page+1;
bRename:false;}
else
this.deletePages(event.target.page+1);
Good try, you are not far off, but there are a couple of errors.
First, the "bRename:false;" line is meaningless. In fact it's a syntax error that will prevent the code from even starting to execute. Delete it. You should have seen this in the console window.
But, the insidious error is this code event.target.page+1
If there is another copy of the check box on the form, i.e., a checkbox with the same field name, then the "page" property will be an array of page numbers, one for each instance of the field. If you know there is only one copy of the field then you're ok, but this something to be aware of. The page property is not always a number.
Last but not least, because it was the point of your post in the first place, the "bRename" argument of the spawn function must be set to false, it's true in your code right now.
Change the spawn line to this:
this.getTemplate("Authorities4-6").spawn(event.target.page+1, false, false);
Otherwise it looks like the code is good to go.