On magento1, I could achieve this by
1, I had my theme folder "mydesign" under frontend/default
2, Another store's folder was also added under frontend/default as "mydesign-en"
3, "mydesign-en" had a template folder under it and there I could have different template files than main store.
4, I applied on the backend configuration under design section "theme setting", for default and skin "mydesign" and for template "mydesign-en".
However, I see the design configuration is different on the backend of Magento2.
At the moment I have mytheme/mydesign under
Do I have to create another child theme as mytheme/mydesign-en to achieve this?