Alas, I have made some substantial progress customising the website.
I now have a customised base.html file which currently overwrites the existing core file. Plus some css stuff. Plus some changes to core files e.g. product_lists, etc.
I read somewhere that if my custom version is copied to frappe/frappe/www this should overide the original?
Or should I wrap up the whole thing in a new app. If so, how do I override the original? Is it by changing hooks.py?