Create a pk3 with the modified file in the pk3 in the same directory structure as it is in the assets files. Drop that pk3 into your /base folder and name it something that comes alphabetically after 'a'.
Then it should work when you startup JKA.
---Jedi Guardian of the Newbie Questions
---Masters of the Force Team Leader / Creator
---Open Jedi Project Lead Moderator / Co-Founder