Ansible: how to set hostname before DNS assigned

hosts

ec2-1-2-3-4.compute-1.amazonaws.com new_hostname=new-hostname.example.com
ec2-5-6-7-8.compute-1.amazonaws.com

playbook-test.yml

---
# Test Playbook for debugging. 
# ansible-playbook -i hosts-test playbook-test.yml -l <group or server name>
- hosts: all
  tasks:
    - name: "Debug hostname"
      debug: msg="inventory_hostname={{ inventory_hostname }}, hostvars[inventory_hostname]['inventory_hostname']={{ hostvars[inventory_hostname]['inventory_hostname'] }}, ansible_hostname={{ ansible_hostname }}, new_hostname={{ new_hostname }}"
      ignore_errors: yes
      when: new_hostname is defined

    - name: "set hostname fact from inventory_hostname"
      set_fact: hostname_to_use={{ inventory_hostname }}

    - name: "set hostname fact from user hostname if defined"
      set_fact: hostname_to_use={{ new_hostname }}
      when: new_hostname is defined

    - name: "show hostname fact"
      debug: msg="hostname_to_use={{ hostname_to_use }}"

results-playbook-test.txt

ansible-playbook -i hosts-test playbook-test.yml

PLAY [all] ********************************************************************

GATHERING FACTS ***************************************************************
ok: [ec2-1-2-3-4.compute-1.amazonaws.com]
ok: [ec2-5-6-7-8.compute-1.amazonaws.com]

TASK: [Debug hostname] ********************************************************
skipping: [ec2-5-6-7-8.compute-1.amazonaws.com]
ok: [ec2-1-2-3-4.compute-1.amazonaws.com] => {
    "msg": "inventory_hostname=ec2-1-2-3-4.compute-1.amazonaws.com, hostvars[inventory_hostname]['inventory_hostname']=ec2-1-2-3-4.compute-1.amazonaws.com, ansible_hostname=domU-01-02-03-04-9C-CA, new_hostname=new-hostname.example.com"
}

TASK: [set hostname fact] *****************************************************
ok: [ec2-1-2-3-4.compute-1.amazonaws.com]
ok: [ec2-5-6-7-8.compute-1.amazonaws.com]

TASK: [set hostname fact] *****************************************************
skipping: [ec2-5-6-7-8.compute-1.amazonaws.com]
ok: [ec2-1-2-3-4.compute-1.amazonaws.com]

TASK: [show hostname fact] ****************************************************
ok: [ec2-5-6-7-8.compute-1.amazonaws.com] => {
    "msg": "testvar1=ec2-5-6-7-8.compute-1.amazonaws.com"
}
ok: [ec2-1-2-3-4.compute-1.amazonaws.com] => {
    "msg": "testvar1=new-hostname.example.com"
}

PLAY RECAP ********************************************************************
ec2-1-2-3-4.compute-1.amazonaws.com         : ok=5    changed=0    unreachable=0    failed=0
ec2-5-6-7-8.compute-1.amazonaws.com         : ok=3    changed=0    unreachable=0    failed=0