Well that's pretty much what us DIY'ers do, unless I've not understood the question
We get a nic base (either % of PG and VG or 100% one or the other) and add flavoring.
It's not as simple if you get higher mg nic base such as 100mg nic which would be very dangerous to inhale so you have to cut it down into a managable mg level such as 12mg or 24 or whatever you prefer.
I vape 30mg
juice and make my own. I typically have a 60mg 60% PG/40% VG base and with the use of some simple math or a
juice calculator I can cut that by 1/2 and offset for any flavorings I use which come in PG.
So a simple 1 flavor, 10% mix would be (using my values above and what I use):
5ml of Nic Base (60mg 60/40 mix)
2ml of PG
2ml of VG
1ml of Flavor @ 10% (100% PG based)
This gives me 10ml of 30mg nic juice with 10% single flavor mix. If you add second and third flavorings or any EM Sweetener you have to offset these amounts to adjust the ratios.
So a 3 flavor mix, at various % of flavor would be:
5ml of Nic Base (60mg 60/40 mix)
1.3ml of PG
2ml of VG
1ml of Flavor @ 10% (100% PG based)
.5ml of Flavor @ 5% (100% PG based)
.2ml of Flavor @ 2% (100% PG based)
This will yield a 10ml of 30mg nic juice with 3 flavors at varying ratios to taste.
Not sure if that answers but essentially that's what we do in DIY. We simple get the base materials and mix them using ratios to find both the correct flavor profile % as well the required nic mg level.