Once you manually take a clustered SQL Server role offline it will stay offline until manually restarted, with this in mind the best way to stop the sql server clustered role is to take the Clustered service offline (will take the agent down too).

Using powershell use

--find service name

Get-ClusterResource | ?{$_.resourcetype -eq "SQL Server"}

--take the service down

Stop-ClusterResource "the sql server resource name"

--to start the clustered instance

Start-ClusterResource "the sql server agent resource name"

How do you expect to stop a service via TSQL from within itself??

You don't want to stop the complete cluster role as you'll need access to the disks so they'll need to be online 😉

It is possible to take the complete cluster down and access the disks via the local node but you really need to know what you're doing here, since you're asking these questions implies you don't and it's beyond the scope of a forum post!!

Test this out on a test cluster first If I were you and when you're happy do it for real