Homestead with specific versions of PHP & MySQL

We will be putting a new team on a project of ours that currently runs on PHP 5.6 and mysql 5.6. I am putting together the homestead box and haven't found a good way to set these versions IN THE Homestead.yaml file. I know I can go in there manually and put these packages in, but I need to be able to distribute only the Homestead.yaml file and not a list of instructions on how to downgrade everything. Here is what I have tried:

ip: "192.168.10.10"
memory: 8096
cpus: 2
provider: virtualbox
name: project_a
ssl: true

authorize: ~/.ssh/id_rsa.pub

keys:
    - ~/.ssh/id_rsa

folders:
    - map: ~/virtualmachines/projecta
      to: /vagrant/projecta


sites:
    - map: projecta.com
      to: /vagrant/projecta/public
      type: apache
      php: "5.6"

databases:
    - projecta

features:
    - mariadb: false
    - ohmyzsh: false
    - webdriver: false
    - mysql8: false
    - php7: false

But it still installs MYSQL 8 and PHP 7.

Is there any way of doing this without manually installing these package requirements or downgrading vagrant (our developers have many vagrant projects)?