@brightranthanks for the detailed response. Perhaps if I share more about my use case it will help.
When a workflow runs in RepoA I want one of the steps to act on RepoB (and RepoC, RepoD, etc). Looking at the action it uses the GITHUB_REPOSITORY env var in the API calls it makes, so I need to be able to override this. I was hoping to use a matrix to store the list of repos to act on.
From a permissions point of view I’ve created a personal access token which has permission to modify all repos that I need, and I can provide that in the config as a secret.