This guide will help you to remove the annoying cheat warning message.
Simple cheats that just let you spawn vehicles should be perfectly stable, but you will still see the warning message every time you save the game.
As an alternative, you can use this mod by xXx2o1o to completely remove the warning message If you don’t want to install any mods, follow this guide to remove this message from your save file.
Download the GTA SA Savegame Editor.
Extract the contents of the .zip file and launch editor.jar (You need Java installed)
CTRL+O to open select your save file. If your game is saved at the first slot, the file you need to choose is GTASAsf1.b (Backup this file in case you break something)
In the general section, you will see a textbox called “Times cheated” Set that to 0 and CTRL+S to save your changes.