1. Custom action can not run any scripts, only the built-in actions.
2. The action "Media: Insert into project" doesn't obey the project settings: "Enable "preserve pitch when changing rate" for new items". No matter you enabled it or not, this setting is always enabled in the item you inserted from Media Explorer with this action.
3. Set as favorite doesn't update the UI, you need to do something else to force it to update.