mysql_thingy defaults.yml

---
mysql_build_cluster: false
mysql_verify_cluster: false

# It's always
mysql_
mysql_
mysql_
# It's never about MEsql
...

mysql_thingy tasks main.yml

---
- include: install_RedHat.yml
  when: ansible_os_family == "RedHat"
  
- include: build_cluster.yml
  when: mysql_build_cluster is defined and mysql_build_cluster
  
- include: verify_cluster.yml
  when: (mysql_verify_cluster is fined and mysql_verify_cluster)
        and
        (mysql_build_cluster is defined and mysql_build_cluster)
...

playbook.yml

---
- hosts: localhost
  connection: local
  gather_facts: true

  roles:
    - {role: mysql_thingy}
    - {role: mysql_thingy, mysql_build_cluster: true, mysql_verify_cluster: true}
...