How to do it...

First, we're going to make a copy of our initial configuration file:

[vagrant@centos2 ~]$ sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config_2020

Then, we're going to make a couple of changes:

[vagrant@centos2 ~]$ sudo sed -i 's#\#Port 22#Port 2020#g' /etc/ssh/sshd_config_2020
[vagrant@centos2 ~]$ sudo sed -i 's#\#PidFile /var/run/sshd.pid#PidFile /var/run/sshd_2020.pid#g' /etc/ssh/sshd_config_2020

Now, we're going to copy our systemd unit file:

[vagrant@centos2 ~]$ sudo cp /usr/lib/systemd/system/sshd.service  /etc/systemd/system/sshd_2020.service

Then, we're going to make some changes here:

[vagrant@centos2 ~]$ sudo sed -i 's#OpenSSH server daemon#OpenSSH server daemon on port 2020#g' /etc/systemd/system/sshd_2020.service
[vagrant@centos2 ~]$ sudo sed -i 's#EnvironmentFile=/etc/sysconfig/sshd#EnvironmentFile=/etc/sysconfig/sshd_2020#g' /etc/systemd/system/sshd_2020.service

Copy the old environment file to a new one:

[vagrant@centos2 ~]$ sudo cp /etc/sysconfig/sshd /etc/sysconfig/sshd_2020

Then, point this environment file to our new configuration file:

[vagrant@centos2 ~]$ sudo sed -i 's#OPTIONS="-u0"#OPTIONS="-u0 -f /etc/ssh/sshd_config_2020"#g' /etc/sysconfig/sshd_2020

Tell SELinux we're going to be running an SSH daemon on 2020:

[vagrant@centos2 ~]$ sudo semanage port -a -t ssh_port_t -p tcp 2020

Tell systemd we've made changes:

[vagrant@centos2 ~]$ sudo systemctl daemon-reload 

Start and enable our second server:

[vagrant@centos2 ~]$ sudo systemctl enable sshd_2020
Created symlink from /etc/systemd/system/multi-user.target.wants/sshd_2020.service to /etc/systemd/system/sshd_2020.service.
[vagrant@centos2 ~]$ sudo systemctl start sshd_2020

Check it's running by SSH'ing from centos1:

[vagrant@centos1 ~]$ ssh 192.168.33.11
The authenticity of host '192.168.33.11 (192.168.33.11)' can't be established.
ECDSA key fingerprint is SHA256:I67oI3+08lhdO2ibnoC+z2hzYtvfi9NQAmGxyzxjsI8.
ECDSA key fingerprint is MD5:03:68:ed:a2:b5:5d:57:88:61:4e:86:28:c3:75:28:fa.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.33.11' (ECDSA) to the list of known hosts.
vagrant@192.168.33.11's password: 
Last login: Thu Aug  9 16:24:50 2018 from 10.0.2.2
[vagrant@centos2 ~]$ logout
Connection to 192.168.33.11 closed.
[vagrant@centos1 ~]$ ssh 192.168.33.11 -p2020
vagrant@192.168.33.11's password: 
Last login: Thu Aug  9 16:40:55 2018 from 192.168.33.10
[vagrant@centos2 ~]$