I can see only one thing that can make it acceptable. First, Al Sev has to be Sorted Slytherin. Second, some time during his first year, Al Sev pulls some truly devious and humiliating prank (probably involving potions) on his arrogant older brother, James Sirius. Third, Slytherin House is so impressed, they declare he should no longer be known by the insipid name of Albus, but shall be known to all Slytherins everywhere as Severus Snape Potter. Fourth, Harry's head explodes the first time he hears his younger son's housemates call him "Sev."