Actually, you can. But it takes EXE hacking if i'm not mistaken.
That is correct. It can be acheived through editing the in-game memory once the game is loaded (i.e. A trainer), or alternatively editing the actual exe.
If you take the memory editing approach, then the memory address of the value (representing the frame limit used when the frame limiter is on) is well known and documented for both games (VC and SA), over in the respective Memory Address topics over at GTAForums.