So your question is
Is there anyway to force the .swf file to accept a new variable each time it is displayed?
Hmm toughy.
For a random one would use
Option a would be using an If Chance function in swish
Something akin to
Code:
onLoad () {
    if (chance(10)) {
        loadVariablesNum("my10.txt",0);
    }
}

What you might do is use the query function in the
object embed to force the load var

src=movie.swf?pageVar=MyVarHERE