hmmm,
correct me if I'm wrong, but the advantage gained from the trimpot is that it makes the base pitch variable? the resistor that's already there sets the clockspeed, but a trimpot would allow you to add resistance if you so desire? if this is the case,why not simply replace the resistor with the trim?

also, are there methods for pitch shifting up? maybe that has something to do with the trim pots.

answer any or none of the above questions,
either way, thanks for sharing your knowlege,

yoni