Since it's just a cover, i'd either try cleaning out the hole really well with alcohol and compressed air and then coating what's left of the threads with JBweld then chase with a bottoming tap after the JB is well cured, or i'd just whack it with a SHARP center punch 2 or 3 times around the edge of the hole.
Neither method is good for structural strength to any degree. But, either will be good enough to keep the cover and screw in place for many years.
I think your resale value will be better with matching cover screws than with one screw head that sticks out to say it doesn't belong.
All that said, if you can find an old retired machinist or gunsmith willing to make you a new, slightly over-sized screw, that will be the invisible remedy. But, it renders proprietary the screw for that hole.
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