I'd read that page layout customization is allowed if you have an enterprise subscription of SharePoint online/Office 365.
Does this mean you can replace any file under /_layouts/? E.g. if we wanted to customize the "delve" page:
http://a**e-my.sharepoint.com/_layouts/15/me.aspx?
Actually it would be sufficient if there was just some way of injecting javascript (e.g. via a customer master page) that could run on any such page and we could do our customizations client-side but replacing the whole .aspx could work too. If this really is possible, how can we push such customizations to an Office 365 site/tenant programmatically?
