Some people are editing texts in this way: decompress package (if it is in compressed state), change text with binary file editor, and then put that package back into the game. If nothing went wrong, game will pick it on startup.
Some tips could be found in this board -
http://www.gildor.org/smf/index.php/board,22.0.html. This is a special board I made on this forum for game editing questions - I can't support everyone there (because I'm not a "modder"), but at least people could share their experience there. I think I'll move this thread there.
Also, because you're asking about UE4 game - the source code of this engine is available for everyone, so it's very easy to modify the engine code to create own tool which will alter UE4 packages. That could be done by programmer with "average" experience (with brains and hands at correct places
)