Is there any way to unlock extra characters in the game?

I know Kitana can be unlocked on the N64 version, does the GOG version have a work around to play as her or others?

Kitana is available only through an unofficial patch/trainer both of which, despite my best efforts, was unable to find.

To unlock Noob Saibot, simply beat the game with Reiko in any difficulty, then on the character select screen, go to the HIDDEN option and select it with RUN. While still holding RUN, scroll over to Reiko (your cursor will start from the HIDDEN button, so just go up, up left) and select him. If done right you'll see Noob Saibot's icon on the tower instead.

Goro works in the same fashion. Beat the game with Shinnok and follow the same steps I explained for Noob Saibot but instead of selecting Reiko, select Shinnok.

I didn't know about the easy fix to get Saibot or Goro, thanks for the heads info!