If you are like me and have gotten out of habit of displaying these while sailing - or haven’t renewed it (yours truly guilty again)-, well, get back in the habit. I got lucky and happened to have come out for a wing swap when the ranger was about to write a warning. Others having too much fun on the water (not naming names) weren’t as lucky.
COVID extension was apparently 7 months - meaning, if your pass expired before Sept 2020, then it is out of that extension period.
You have been warned - proceed at your own peril! 
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Renewals are available at the gate kiosks. Make a copy of your receipt (to display until your new hang tag arrives) and mail in the original to the Corps for your new pass. Easy peasy - takes about a week.
Directions towards the bottom of this page: https://www.sam.usace.army.mil/Missions/Civil-Works/Recreation/Passes/
Their office is still closed. This is the only way I know of to do it unless any of the manned stations do it on weekends (which I doubt).
Yep, I paid and got my temp receipt while the ranger was waiting with pen and warning paper ready to be filled.