You could taper the calmag down to near zero by harvest but like Mr. G said, both are needed to at least some degree until the end.

if you truly believe you are getting Calcium deficiency and it isn’t from a lockout, I wouldn’t cut it out personally..

I believe flushing nutrients only makes good sense if you have some kind of excess. I have very little to back that up. Either way, if you ARE out of calcium, certainly no reason to be flushing it out specifically right? Imagine a plant that had zero nitrogen by harvest. Would it taste awesome? Perhaps, but not really because you’d be harvesting a dead plant 😉