If you build a good living organic soil (LOS) you should be good all the way through harvest with a bit of top-dressing along the way. Some are really complicated with 10+ different ingredients to source and some are as simple as Retrix's current mix that's working well for him:
2 CU ft of Fox Farm Happy Frog.
2 Cups of build-a-soil Craft Blend Nutrient pack
4 Cups of build-a-soil Mineral Kit for Peatmoss
He's not in flower yet but top-dressing with earthworm castings and some other organics will probably do it.
That said, I can tell you that the transition from blurple to white can be hard on plants having seen a number of grows go sideways with deficiencies when switched midstream, including my Sour G.
I think the most important thing is not to get hung up on organic this or LOS that. Most important is to get the plant what it needs and not turn a great grow into a crispy one by hanging onto the ideal of what type of grow it is. If you can find organic cal-mag that's great, but if the plants start showing you deficiencies, give them what they need however you can, and worry about correcting the soil construction or the trueness of the organic grow on the next one when you can get it more dialed in or won't be switching lights in the middle.
\rant