Yes, you can add 1/2 of each to reach 0.8ml or premix the two and have 72mg 50/50.
If you are not adding any additional PG and you feel that your mixes are too thick or do not have enough throat hit you can use more of the PG Nic and less of the VG Nic.
The recipe you’re looking at has the amount used by the creator of that recipe. The nic they used just happened to be 100mg 50/50. When you go into adapt this recipe you input the desired strength you want to make 1.5mg 3mg 6mg etc… Then further down where it say nicotine strength you put in 72mg, which is what you have. Then for PG content of nicotine you put in 100 (if you use your pg nic). If you decide to use your VG nic you put 100 in for VG content of nicotine.
I wouldn’t think it makes any difference unless you’re intolerant to pg or you want to make a high vg juice. Someone with more experience could chime in here but if I was you I would just use whatever nic you wanted to.
I agree with DrChud, I don’t think it would matter if the nic is pg or vg based. The amount of pg or vg you would add adjusts accordingly so the final result of the juice would still be 50/50 pg/vg with a nic strength of 3mg. When you click on Adapt recipe to change the strength, also change the pg or vg content to what you are using.
PG is a better carrier of flavor than VG. Whereas VG is better at creating more vapor. So your juice being a 70/30 vs 90/10 will vary in flavor and amount of vapor. Make recipes at the ratio you prefer.