I would agree with others and recommend using the preview period (Publish to Prebid review/bidding start time). If your event(s) should not allow any pre-bids, you can set the event rule to not allow pre-bids. No all this is done to give vendors/participants to view details of your event. If I can read between the lines, you are looking for just a heads up message to vendors/participants without wanting to give any details about the event but there exists no such functionality but you may use a workaround but at your own risk.
1. Create a test event with minimum mandatory details and publish it
2. Use message board for notifications
3. Once the content and other details are finalized, complete the event by editing it
4. Publish all final changes along with setting the test project parameter to "NO"
Note: Using this approach can confuse participants in real/test events especially the new ones and may create chaos!!