Yes, you can pause and turn off slice flex anytime.
When you pause it, slice flex stops creating new FDs. Your existing FDs continue earning 6% p.a., renew automatically and remain available for your payments. You can resume slice flex again whenever you want.
When you close it, slice flex stops creating new FDs and your existing FDs are broken and all money is transferred to your current account and now nothing of it earns any interest.