[imglorp]

You can treat the ISP's router as bare, hostile internet and put the router of choice behind it. Disable their WIFI if you can, but don't use it. Plug an ethernet cable from your router's WAN port to one of the ISP router's LAN ports. Your router's WAN side will get one DHCP address from the ISP's router. Your LAN side and firewall rules are however you like them, on your router. This whole thing is called "double NAT-ing" -- search for that term for a how to guide.

[XelNika]

A lot of ISP routers have the option to disable everything except the modem, often called "bridge mode". Avoids double NAT.

[jorvi]

You can also call your ISP to put the modem-router in bridge mode. This will basically turn off all of its features and just have it pipe internet access from its LAN ports. If you do this, remember to go ISP router LAN port > personal router WAN port, as you won't be protected by the ISP router firewall anymore.

[AzzieElbab]

Good suggestions. Thank you. I have done something similar before. Only problem is, I had to revert the setup each time isp had hiccups otherwise they refused to provide any support