Yes, you can, but it will take more than a drop depending on how much
juice you have. If you have a large bottle of this
juice, transfer some to a smaller bottle and try flavoring this sample.
I would try adding 2% flavoring, then letting it sit for at least 24 hrs. to 'steep'. Shaking the bottle occasionally helps it become mixed.
One drop from my FlavourArt bottles equals 0.03mL.
If you had a 6mL sample to flavor up, then: 6mL x 0.02 (2%) = 0.12mL, which would be about 4 drops of flavoring.