I have never heard of varicose veins on the breast before. I would call and ask my Ob/Gyn.
If you already have the vein damage, I don't know if changing your pumping habits would do anything for you other than to stop any more vein damage. Besides, you are getting close to the winding down phase of needing breastmilk as your child starts eating solid food and learning to drink from a sippy cup.
I have very fair skin, and since starting breast-feeding I have noticed that the veins in my chest and breasts have gotten more prominent. Sometimes the veins will even bulge a little, especially when I am closer to engorgement.