Features used to implement the example
Example: Add watchers from a part of the issue summary: "Summary_text - watcher1, watcher2, watcher3, ..."
As in my answer to your previous question you should move the post-function below "Creates issue originally".
On the other hand to add as watchers the list of comma separated users in summary, you should remove the previous part of the summary with post-function Regular expression renderer. I show you exactly how to do it:
Use post-function Copy parsed text to a field to copy "Summary" to an auxiliary field (Ephemeral string 1) that can be modified in second step by Regular expression renderer
Use post-function Regular expression renderer to remove the part of the summary preceding the comma separated list of users. We use "Ephemeral string 2" as replacement string because it isn't initialized. Regular expression utilized is "^.*-\s"
Use post-function Add or remove watchers to add users in "Ephemeral string 1" as issue watchers:
Once configured "Create Issue" transition looks like this:
