Using variables for system prompt in prompt.yml?

[mrochon]

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Is there any way to use a variable, e.g. {{myField}} in the system prompt in the yml file? I would like to test and compare my prompts using the comparer functionality but at run-time my code needs to dynamically replace certain values in the system prompt. I can obviously have my code look and replace a fixed value used in the yaml prompt but that make for somewhat in-elegant code. Here is what I would ideally like to do:

...
messages:
  - role: system
    content: >-
      Create oData filter expressions using {{field_names}}...

  - variables:
    filter_names: Age, Name, ...