You can't access the seed value right now (and have not been able to in the past). The seed value is randomized when the emitter is added from the library.
So if the emitter has been modified at all from its library version, you'll have to add it to a library temporarily (or a junk library), then use the "replace" function. Actually, I just tried this and it does not work -- the emitter retains it's seed value.
Only thing I can suggest is to tweak some values (number, velocity, or something else) to get the particles to "readjust". If the emitter uses a non-zero preload value, changing that will work too.