How do I update the template in a content composer control block?
Sooo... how does one change the default template of a composer block
Have you tried to go to "Pages & Themes / Page Types" in the dashboard, and here chose "Basic Details" for your page type. You should be able to set things regarding page templates there.
The problem was I can't apply a custom template to a composer block.
My temporary fix was to edit the default template in the block as that is the only template the composer block will call, but obviously this is not a long term solution.
I understand now...
Go to "Pages & Themes / Page Types" in the dashboard. Here chose "Output" for the page type you want to edit. Then on the template page Click on the "Edit Defaults" on the right. Then you will be able to put the Default page type in to edit, and you will be able to assign a custom template to your block.
Unfortunately this is exactly what I did. Maybe I did not explain it the best way in my original post... but when I said "... edit defaults of page type I can change the template in "design and custom template" for the composer block" I should have also said that I got to that page by going to Pages & Themes -> Page Types -> Problog Post -> Right Sidebar -> Output -> Edit Defaults ... and then in that page I edited the block that says "The Content page type composer form element will output its contents here (Block ID 14)" and selected "design and custom template" and in there selected the new template.
I'm sorry that I can't help you!