The juice spill is called accidental damage, and if not covered under your warranty, it would be blamed for any manufacturer defect that would be covered, so you have a problem. It happens that MacBooks are badly overpriced for performance and I dislike the company for their huge profits on the laptops that are not nearly worth the price, and you will pay a lot of money for Apple to replace the Lenovo Keyboard and clean the motherboard that may fail later from the juice spill.
Yes, replacing the keyboard yourself also may have a warranty void, but it may not be sticker sealed and the do it yourself would be buying a new keyboard and replacing it, and determining whether the motherboard also got juice on it.
If you had a Lenovo Thinkpad, which is quality hardware, most have a spill tray protecting the motherboard and the Lenovo Thinkpad Keyboard is easy to replace.