Hi,
It's becomes the same result as if you were long the shares, & is effective the day after the split date. Your acct. will reflect the split shares in whatever increment they're split, with price adjusted accordingly. 2 for 1, 2x as many, & 1/2 the cost, 3 for 2 = 1.5x as many, & 2/3s the cost, etc.
Been the recipient of many of these, so I'm speaking from experience, from the long & short side.
Good Luck with Your Trade!
God Bless & GFtY! Kelly