Unfortunately, there is no specific cheat code in GTA San Andreas designed to bypass missions. However, there are alternative methods you can explore to skip or overcome challenging missions. Here are some options:
Fail the mission three times: If you fail a mission three consecutive times, you will have the option to skip that particular mission or part of it. On Xbox, press the "X" button, and on PlayStation, press the "Square" button [1].
Utilize the Mission Passers tool: You can use a third-party tool called "Mission Passers" to skip missions by replacing the main.scm file in the Script folder of your San Andreas directory. It's crucial to back up the original file before making any changes. Note that this method may lead to crashes when using the V2 version of the game [2].
Use save files: Another alternative is to download save files from the internet where specific missions are already completed. Various save files are available with individual missions passed. Ensure to select the appropriate save file based on your game version (V1 or V2) [2].
Engage with the community: If you encounter difficulties in completing a mission, you can seek help from the GTA San Andreas community. You have the option to upload your save file and request assistance in the Mission Help forum. Other players may assist in completing the mission on your behalf [2].
For further information, you can refer to the following resources: