Custom expression/function in Yaml

[FreesonM3as]

Hope to be able to provide a custom function in yaml by a Azure DevOps Extension contribution point.
For example:

- template: sometemplate.yaml
  parameters:
     parameterContext: ${{ merge(parameters.parameterContext, convertFromJson('{"dryRun":true}') ) }}

where merge and convertFromJson are custom functions.

[max-zaytsev]

Please post your suggestion on the Developer Community to get the right eyes on it, since this repo is mostly for questions about templates located in this repo.