Can you feed a baby guinea pig lactose free milk?

NO , please do not do this.

you only give guinea pigs milk if you have to like if the mother has rejected it and it is under 4 weeks of age. but if your guinea pig is over 4 weeks of age, then you have no need to feed it any sort of milk at all. But if your guinea pig is under 4 weeks and it's mother is no longer with it, pure goats milk is the best for it.

Hope this helps.