removing temple veins will have no effect, no untoward effects on the appearance or size of a forehead vein. The veinous drainage of the face and scalp is very rich and there is no physiologic detriment or detrimental effect in terms of causing congestion on remaining veins in the forehead, face, etc.
The forehead has a vast array of veins which drain through many channels. Treating temporal veins by either excision, laser or sclerotherapy or any other method will not cause other veins or center forehead veins to enlarge. It is the same principle as in treating spider leg veins. Treating these veins in one leg area does not cause more veins to grow elsewhere (unless there is an underlying saphenous vein reflux problem).