Ive always been one to keep my leaves green as well. I think its easier in soil, I dont feed any N during bloom, other then small amounts in my micro blend, and this time using some molasses. But theres enough in the soil, and the plant to make it thru without yellow leaves. I dont need them dark army green, but I understand that sunleaves give the plant its energy to grow buds.
My fear of giving more N during bloom is that excess would certainly decrease its flowering. So I "give it what it needs", and it doesnt need any more N, cus it stays green... Its more difficult to tell how much P-K they need. IMO you dont see they need more till they are very deficient. So I wanna make sure they have plenty.
I also would like to point out the fact that everyone gets so caught up in the numbers of the NPK, but its the ratio thats more important. A 10-50-10 is the same as a 1-5-1, its how much and often you use it. And also what form of N and how available the nutrients are.
I use fish emulsion 5-1-1 during veg and a bit off micros, and 0-10-10 during bloom. This growt Im using bat guano 0.5-12-0.2 early bloom and a bit of molasses at veg and bloom. Also I mix a bit of 5-5-5 into the soil before planting.
I like organics for a few reasons, but my fear in potting soil is that they might not be readily available to plants like chems are. In native soil, microbes break them down and turn them into usable plant food. But potting soil Im not so sure. Potting soil is mostly wood and peat, things that microbes would also have to break down to turn into plant food.... Its the whole nitrogen/carbon cycle...