Combine pi-hole and nxfilter on 1 raspberry pi 4

Question

Given I have a raspberry pi 4 with Raspbian Buster, I would like to combine pi-hole (for adblocking) and nxfilter (for parental controls).

I could specify nxfilter as the upstream dns server for pi-hole or vice versa.

Problem is, both services use port 53 and I cannot see an option in either to change their port. For nxfilter however, I could change the listen-ip address, which in turn leads me to believe that if I can assign an additional ip address to the raspberry, I could have nxfilter listen on the additional ip only, resolving the conflict regarding port 53.

Right now the raspberry receives a dynamic address from the dhcp server (fixed assigned ip however).

So the question is: how do I assign an additional static ip address to the raspberry?