to use a custom alert sound you must create a directory called "TauntAware_CustomSounds" in your addons directory
(i.e. c:\users\public\games\World of Warcraft\Interface\Addons\TauntAware_CustomSounds") 
and put the "custom.mp3" or "custom.ogg" in that directory

if you replace one of the supplied sounds in the addon directory then when the addon gets updated by the curse client the
sound files you replaced will be overwritten. This is the only way to prevent that and still use an automatic update client.

you can then select that sound from the command line or control panel plugin
just pick a command line

 /ta alertsound custom.mp3
 /ta alertsound custom.ogg
 /ta config