Sure, it plays no role in the ferment (being unfermentable), don’t know if you have used much Lactose before but it’s not very sweet.
Arguably at the end of the ferment or during packaging would be the best time to add Lactose, it may not be fermentable but it is a sugar and increases the osmotic pressure on the yeast. Anything we can do to take any stress off the yeast is a good thing.
Mark