If you take open source MongoDB and add 10 lines of custom proprietary code, is it still MongoDB? What about a hundred, or a thousand, or a million? What if you

If you take open source MongoDB and add 10 lines of custom proprietary code, is it still MongoDB? What about a hundred, or a thousand, or a million? What if you change the interface? Ultimately you can give the modified service any name you want, and whether it is "actually MongoDB" or not is a subjective judgement.