Is this possible, with a server like Apache or perhaps using PHP? I would want to use the site to serve various webpages from the internet but to override CSS and JS in the pages. Hopefully it would be possible to allow continuous web surfing within the site's page too.

It has been a while since I have programmed webpages so I can't quite wrap my head round this right now... maybe it is obvious.

What approach would you take? thanks