When I first posed this question to my Broker, their reply turned out to be plain wrong. Tech Support said if I am holding 1 Long MES contract overnight, and then place 1 Short MES Order the next day, when it triggers it will simply close the Long position I was holding overnight. If this had turned out to be true, I would not be able to keep my Swing trades separate from my Intraday trades.
After contacting their Trade Desk however, I got the correct information (which by the way agrees with how Will described this during our 7/28/20 Live Training session – no surprise there). Here is the correct answer - which came from the Trade Desk:
The oldest position would continue to carry per exchange regulations. If you carry 1 long into the day then sell 1, the exchange requires clearing of the Intraday trades thus carrying the original long into the next day.
What that answer is saying is if I am holding 1 Long MES contract (my Swing position), then the next day I open a 1 MES contract Short position, then close that Short before the session ends (my Intraday trade), then my Long position will remain in effect. This confirms that I will be able to manage Swing and Intraday trades at the same time.