Temporary routes can be added using the following command on CentOS7

Simple route:

ip route 10.10.20.0/32 via 192.168.20.1

Device based simple route:

ip route 10.10.20.0/32 via 192.168.20.1 dev ens1002

Device based simple route with specified metric:

ip route 10.10.20.0/32 via 192.168.20.1 dev ens1002 metric 105