Funnily enough, I'm sitting here working on a file that does more or less the same thing. Here's one way to stop the text file caching:
myText.load(txtInput+"?noCache=" + random(99999)+random(99999),0);
Basically, as long as you put a unique number at the end Flash will be forced to load a new copy and not use the cached file. You can generate the random numbers any way you want, but this one works well.
(I just realised that code is a paste from my own file - it's a normal loadVars object).
As long as this is executed (from your clip event - or based on a returned variable 'trigger') it will load the updated variables.