This class of programs absolutely still exists (see: every debugger, scanmem, GameConqueror, etc.).
Sandboxing doesn't prevent processes from inspecting the memory of other processes, it just prevents the sandboxed process from doing things it shouldn't.
https://en.wikipedia.org/wiki/Game_Genie
They really markted that well has having to enter codes, but of course, they were just ROM addresses + values to pretend to be at those addresses.