How do I redirect URL while also changing source and destination IP address over HTTPS?
Solution 1:
I don't see why you would need iptables over here.
Just install a server as a reverse proxy, have that server's IP in the whitelisted IPs. End-users will connect to that server, which will reverse proxy connections to the final destination.
A reverse proxy opens a connection from its own IP address to the proxied server IP address, so you don't need any extra tricks for IP addresses.