Hi
You don't have that level of control. A stack is a stack, and all admin is unified accross the stack.
You can VLAN off the third switch, create a VLAN interface and a DHCP pool that correspond, and DHCP will work.
You can't segregate the third switch off at the management level though - you may want to ensure that the SVI that you need for DHCP to work on the switch is configured not to allow non-DHCP traffic.
Alternately run DHCP on a device in that VLAN rather than the stack if you want it to be more completely seperate.
Regards
Aaron
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Aaron
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