PS I just did it and it works. In the default file the ipv4 section is
[ipv4]
method=auto
I changed mine to
[ipv4]
method=manual
dns=192.168.20.126
addresses1=192.168.20.200/24;192.168.20.1;
where 20.1 is my gateway and 20.200 is the address i wanted, 20.126 is my dns server. Note the semicolons, especially at the end of the addresses1 line.