How can i edit proxy error page display on Router OS ver 4.4?

Also to block adsense on any url like http://www.xc.com/adsense/support....

Your respond is highly welcome.

Edit webproxy/error.html. If it doesn't exist, go into the web proxy settings and click "Reset HTML".

For blocking access to certain URLs read http://wiki.mikrotik.com/wiki/IP/Proxy#Access_List