You can always add stuff to a mix, including nicotine.
Taking stuff out , not so easy.
Yeah, I assumed that the mixing calc was done beforehand and the final ingredient going in later. For whatever reason, perhaps to get steeping underway if he has no nic.Although it won't make much difference, seeing as the quantities of the addition will be small, you might like to consider the dilution effect to the flavour and increase your flavouring proportionally at the mixing stage? Doubt it will be much of a big deal, all depends upon how fastidious your are.
I wouldn't worry about it ... do the calculation for the full 100mls, mix it all up and leave the nic to be added later. Just leave a note to remind you how much nic has to be added to that bottle.lol thanks for all the replies. I was actually having a think about it after and yes many other things came up.....it won't steep well without the nic........then there was the issue of the calculating the nic to be added later.
Hmmm guess I should just nice steep it normally with the nic.