I mix lots of flavors. The nicotine doesn't add - it's averages since it is per ml. So if I mix equal parts of 18mg and 10mg
juice then I end up with 28/2 = 14mg juice.
I regularly use two vanillas mixed together - I mix them right in the cartomizer. And I have a 50PG/50VG juice I love but that juice is thicker than I like to put in cartos so I mix it with a similar flavored 100% PG liquid to thin it. I have old juices that are higher nicotine than what I now vape, so I bought 0mg of the same juices and I mix them just to lower the nicotine. And I have some "mixer" eliquids I use to save bad flavors. One mixer is a good sweet vanilla
eliquid and it is good for fixing up any fruit or dessert flavor I don't like.