Meltdown Patching can be turned on as needed Experts,

Need to know if anyone has witnessed or found such settings while patching SQL servers for Meltdown patches.

Our sys admins informed that OS patches for Meltdown can be turned ON/OFF bases on registry setting and can be enabled or disabled.

Just looking if someone know a similar way available for SQL server patches? Means you can turn it active when needed?
No, there is no publicly known way to do this for the SQL Server Meltdown/Spectre patches.

Microsoft might have a trace flag to do it, but if so, they haven't shared it publicly as of yet.