you can't change your name mid run can you? so i'd think it means per savefile
no-no, after you use it the first time, it throws you back into the point spending screen, so you can actually spend those points, so after you do, you get to... pick your name again,
for real this time. and if you choose the joke name again, the game makes a big fuzz of it, but ultimately gives you another 50 points.
After you spend those points, the game lets you choose the name yet another time, but this time there is no bonus, just some jokes here and there. so I wonder, if you finish that run and pick a name again, would that matter? Honestly, that would not even have been that big of a boost, I had runs with 4000+ points acquired.