Themes

I don't think you can create a new page type, but what I have done in the past is to use a conditional statement based on the page type
If pagetype = enrol-index { do this code }
else { do standard incourse layout code }

OR
If the changes can be done in css, rather than needing html/php changes, then you can just use the body class created by the page type. You can do a lot with bootstrap by overriding the css, including layouts