Zentayl 2.x came with the caching Proxy Squid - i want to use squid as caching proxy for the local lan and as reverse proxy for the wan(internet)
Unless I'm wrong, meaning of "reverse proxy" is not to act as a proxy relaying your HTTP request to internet. This is what a basic proxy does.
Thus if I rephrase your request, you would like to use Squid as proxy cache for intranet and proxy (with cache too?) for internet. Am I correct? If yes, why does it required template changes?
Reverse proxy is somewhat different: this configuration allows hiding all your web servers behind proxy server that will redirect all users request toward the right server while exposing only one IP to internet (or internally in case you have internal reverse proxy).
It is not very different from standard proxy but I would say that proxy deals with outgoing requests while reverse proxy deals with incoming requests.
So, is it really "reverse proxy" that you need to configure?