Not sure what you are asking, try to be clear for your audience, (just a tip), if you are asking if you can add cal/mag after you feed, I think it would depend on how you are growing. Are you DWC or soil?
If in soil, because that is what I know, I don't think it would be a problem in my garden to add cal/mag after feeding, if I chose to do so.
That's all i can give you for now, and off the cuff.