Force "check mode" for single task

Need to run some preparation tasks on your host in case of package update?

You can trick Ansible to run single task in check mode to predict the result
with check_mode: yes parameter:

- name: "(CHECK MODE!) Need to update docker-engine?"
  apt:
    name: docker-engine
    state: latest
  check_mode: yes
  register: apt_check

- name: "Remove ourselves from load balancer before update"
  command: "/opt/bin/remove_host_from_balancer.sh {{ inventory_hostname }}"
  delegate_to: balancer
  when: apt_check | changed

- name: "Update docker-engine"
  apt:
    name: docker-engine
    state: latest
  register: apt_res

- name: "Enable ourselves on balancer"
  command: "/opt/bin/add_host_to_balancer.sh {{ inventory_hostname }}"
  delegate_to: balancer
  when: apt_res | changed