Yes I know it's really stupid but if anyone re it was a hentai one-shot about switching partners,it was 4 people and they weren't even couples at the beginning of the story.Also one girl was definitely a blonde and the other probably a brunette,the title even had sth to do about switching partners but I can't what exactly 5l2c65

Could be :
by Hissatsukun - Swap on the Beach

Or maybe ?
by Naruco Hanaharu - namadashi generation (but they are lovers and no blonde)
by Kawasaki Tadataka - Rock, Paper, Scissors (More or less lovers at beginning too)
by Kisen - Sex Share (lovers too and not really blond for the 2nde girl)