Add music AttributeExtensions to HoldCall

Hey,

I registered a new IElementOfCommand Class after HoldCall for the InteractionVoiceHoldCall chain.
How can I add or edit the music attribute, to change the hold music now or am I on the completly wrong track?

Code for the registration

IList<CommandActivator> commandList = new List<CommandActivator>();
            commandList.Add(new CommandActivator() { CommandType = typeof(BeforeEventHeldCommand), Name = "BeforeEventHeld" });
            commandManager.InsertCommandToChainOfCommandAfter("InteractionVoiceHoldCall", "HoldCall", commandList);