If you are talking about  a lily plant that grows from a bulb, then no you cannot cut the bulb in half. You can wait until fall when the foliage of the lily is turning yellow then dig up the plant roots and all and separate any side bulbs that cling to the mother bulbs. Then you  move these baby or smaller bulbs to a new area and leave the mother bulb in place. You can also try pushing a shovel into the clump near the sides of the mother plant and moving the entire shovel full of soil and roots to a new location. Keep growing, Marianne Binetti