Yes, it is.  I'm using similar functionality to prevent folks from publishing locked [by others] content in MyLocks.  The magic starts at the ApplicationEventHandler.

    public class ApplicationEventHandler : IApplicationEventHandler
    {

        ...
       
        public void OnApplicationStarting(UmbracoApplicationBase umbracoApplication,
                                          ApplicationContext applicationContext)
        {

            // Tap into events that locking would affect
            PublishingStrategy.Publishing += (sender, e) =>
                {
                    if (e.CanCancel && MyLockStorage.HasLockedContent(e.PublishedEntities))
                        e.Cancel = true;
                };

            ContentService.Publishing += (sender, e) =>
                {
                    if (e.CanCancel && MyLockStorage.HasLockedContent(e.PublishedEntities))
                        e.Cancel = true;
                };

        }
    } 

However, now the big let down.  You can't override the message when cancelling a publish event, you'll only get the "Cancelled by 3rd party..etc..etc..".  If you can figure out how to intercept the message and put in your own, I would be keenly interested in it, but for the time being I don't believe what you are wanting to do is feasible with the current codebase without modifying the core or some hellacious hack.

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