It depends upon how you feel about having a frame with a warranty, which you mentioned. However, if there was any one place on a frame, other than the steerer tube, that I had to trim, trimming that location would make me the least nervous. Just make sure the cut is clean and properly finished. I would also put duct or masking tape on nearby areas of the frame to avoid unwanted damage.
Pete
Last edited by mudboy; 09-10-10 at 08:26 AM.
Reason: thought it was a CF frame, it's Al.