you cannot SET values for the Local Director through SNMP. Just GET them.
There used to be a GUI for the LD, that works up to version 3.x. It no longer works in version 4.x. The name for it is CVS and it can take servers out of service. It does it by telnetting to the LD and issueing commands.
Also, the LD support Dynamic Feedback Protocol (DFP) which is a protocol that allows the LD to talk to an agent application (installed on the server) and can dynamically adjust the server weight according to load.
Hope that helps,
-Steve