Is there a console command or whatever that can change your Shift-A car sound set? I've looked everywhere and tried everything that seemed logical but to no avail. Any help is appreciated.
no there is no command for this. If you want to automate it with single keystroke you will have to use a technique employed in the FLIPCAMS mod for LFS.
It uses msdos batch files (which can be called from LFS) to rename files in the LFS directories, (the sound files in this case) then after the file has been moved/renamed then initiate a /shift W keypress to re-init the sounds.