Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. 
Using a text editor, edit the "User" file in the game directory. Edit the file to match the desired weapons. If needed, use one of the text files in the "Variants" sub-directory as a template.

Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. 
Reach the end of mission screen with the customize, quit, and continue options. Then, press [Alt] + [Tab] to return to Windows. Use Windows Explorer to enter the "Variant" sub-directory in the game directory. The files in this directory represent various vehicles in the game. A text editor can be used to view the contents. After selecting a new vehicle from one of the "Variant" files, copy that file into the main game directory. Delete the "User" file in the main game directory, then rename the copied "Variant" file to "User". Press [Alt] + [Tab] to resume the game with the new vehicle.