Question

Hello Rabbi, let me begin with gratitude for all the lectures you upload to YouTube, and also for all the books of yours that I’ve read—many of them. I’ve learned a great deal thanks to you.
I wanted to ask: what is the law in a case where the reason for a Torah commandment has ceased to exist—does the commandment itself also cease? Suppose Maimonides gives a reason for a commandment, and that reason no longer applies today. Would the commandment be nullified, at least according to his view? Or do we say: even if the reason has lapsed, the enactment has not lapsed—as we say regarding rabbinic commandments? I need some kind of proof for this.
And of course, the question is about a case where the reason has definitely ceased, not like what we find with Solomon, who said: “I will take many wives and I will not turn astray.”
For example, the Sefer HaChinukh in the portion of Re’eh wrote regarding the reason for the commandment of slaughter: “A further reason given for slaughtering from the neck with an inspected knife is so as not to cause animals excessive suffering, for the Torah permitted them to man for his benefit, to be nourished by them and for all his needs, and not to cause them gratuitous pain; and the sages have already spoken at length about the prohibition of causing suffering to animals… and they concluded, apparently, that it is a Torah-level prohibition.”
If we assume that today the commandment of slaughter causes a great deal of suffering to the animal, then according to his view should one slaughter by a different technique, or look for a different reason for the Torah’s commandment?
That’s just an example, but I’d be happy if the answer were not about the example itself, but rather a general discussion of whether “when the reason is gone, the enactment is not gone” applies to Torah commandments.
Thank you very much, and Sabbath peace.