Dilution is your friend, if you want a custom low concentration.
The easiest way to do a dilution is probably as follows;
First, identify your two (or
three) sources, which would be;
1) A nic source whose mg amount is "too high"
2) A non-nic flavored source.
3) (optional) pure unflavored VG, to cut back on the flavor, if desired.
Assuming for the moment you don't want to cut the flavor, here's the steps.
First, identify the amount of nic in the nic source. In the example Scottbee gives, that would be the 26 mg.
Second, decide what amount of nic you want. I'll take 8 mg (middle of your 6-10 range) as an example.
The mixture ratio you should use with those calculations is:
* 8 (your desired concentration) parts of the high nic source
* 18 parts the zero-nic source for dilution.
Why 18? Because your nic source is 26 mg, and your desired amount at the end is 8. 26 minus 8 is 18.
This works for any amount, and for any source, as long as the source is higher than your final amount, and the worst bit of math you have to do using this method is simple subtraction (for the math-phobic out there)
Now, what if you wanted to cut the flavor a bit? Simply substitute a few parts of pure VG for the flavored 0 nic VG - for the nic calculation purposes, those two liquids will be identical (both are zero-nic). How much you substitute is up to you, depending on how "strong" the flavor of the original is. If you like the flavor strong, of course, then don't use any straight-VG.