support for variables inside parallelCluster yaml configuration

I have seen example configurations where certain items, such as HeadNode.Ssh.KeyName or HeadNode.CustomActions.OnNodeConfigured.Script, need to be modified for specific use cases or cluster instances. These items are currently distributed throughout the yaml files. Is it possible to define variables for such items at the top of the yaml file, then refer to variable names throughout the yaml document. I am thinking of a syntax similar to ansible variables or, in terms of a (hypothetical) parallelCluster configuration

Vars:
  ssh_key_name: key123
  postinstall_path: s3://example123/postinstall.sh
[..]
HeadNode:
  Ssh:
    KeyName: "{{ ssh_key_name }}" 
  CustomActions:
    OnNodeConfigured:
      Script: "{{ postinstall_path }}"

Support for variables would allow one to focus on the top of the yaml configuration during adjustments for specific use cases instead of having to comb through the entire configuration.