So I'm writing a script today and it uses SKSE's function Game.ModPerkPoints(int).

It worked in a script I wrote about a month ago. Today, when I try to compile, I'm getting this message:

ModPerkPoints is not a function or does not exist
cannot call the member function ModPerkPoints alone or on a type, must call it on a variable

I'm 100% certain my syntax is right, I copied it right out of the script that compiled OK. Did this function get deprecated?

There was a recent Dragonborn CK update that added the source code for the scripts. This reset the INI files for some, and all of the PSC files for others. Try re-downloading the SKSE PSC files in case they got overridden.