You would have to have a shoe repair shop evaluate them - some heels are hollow except at the tip so you might not be able to shorten them and retain the necessary strength - others are solid, so he would have to look at them. Might be able to just remove heel cap, cut down, and put heel cap back on.
Bear in mind that cutting the heels down will rock the shoe "backwards", so you will be walking on sole further back on the shoe - if the unthickened sole part betweenthe heel and the ball of the foot would be walked on because of this, you might have to pay him to add leather there to, which might mean resoling the entire shoe - could get pricey, if these are not worth hundreds of $.
As for evaluating a shoe repai place - only thing I can think is if these are pricey shoes, call store and see if they recommend a particular place. Otherwise Search Angies List for sheo repair places and reviews.
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