One would think any nipple work would impact sensation. However, in looking up "nipple reduction" on cosmetic surgery sites (not necessarily FTM-specific), I have come across the following statements:
"There are many methods used by various surgeons, including removal of just the top of the nipple, which is then closed with tiny incisions. Nipple reduction may also involve removing a cylinder of skin around the neck of the nipple, then pushing the nipple back into the breast tissue and suturing the skin closed. Sensation is almost always normal following a nipple reduction"
"Very prominent nipples can be reduced while retaining sensation with a simple office procedure performed under local anesthesia. The scars are virtually undetectable and the results are very predictable."
If anyone wants the actual links to the sites, PM me. It all sounds promising, though I don't know if by 'retaining sensation' they mean tactile or erotic sensation.