Is it possible to have a particle effect that you can pause on touch, rescale as the user resizes the screen zoom, move as the user moves the screen center point, and can then be resumed at the different scale and relative position on screen?

There shouldn't be any problem. Individual particles aren't processed / drawn while the particle engine is set to pause, but you can always edit or set any parameters, scale Emitters etc. Changes that are affecting animated particle properties will be visible as soon as you unpause the engine and the particles are processed again.