My ISP uses a Carrier Grade NAT (a switch inbetween ISP line and my primary router) and that doesn't allow me to do portforwarding (I have set it up but to no use). After much contemplation, I have decided to go for a VPN. On doing some research, I came to know that you can have two routes using iptables based on the direction of your connection.
Apparently, the converse of what I need seems to be here (Incoming/Outgoing seperation for VPN).
Will this setup even work for stuff like torrents and perhaps extend couple of services from my home network? How can I implement this in my home network?
P.S: Based on the idea given by @roaima, I followed this guide to setup two routes with the VPN route being used by vpn user. This is the detailed guide to follow. http://www.htpcguides.com/configure-transmission-for-vpn-split-tunneling-ubuntu-16-04-debian-8/