Staying on an earlier version is not ideal as some of the later microcode updates actually contain useful errata beyond performance-limiting mitigations. Really wish Windows had an option like "mitigations=off" in Linux.
Yes, I assume the kernel has a predetermined list of microcode to be disabled when the flag is set. The same should be doable in Windows right now but the process seems quite tedious.
The kernel keeps no such list and microcode is a monolithic firmware anyways so having such a list wouldn't enable you to pick and choose which fixes you get to apply.
