In a multi-master system, you can set one or more masters to be optional. 

This can be set on any master except the headmaster, the module with address 0. 

If the MD4 is optional and the MC42 is standard, you can set the MC42 to address 0. This will be a limitation for the connectivity security properties. The option "Ask user" on the properties "allow remote connection" and "allow remote stop" will only work if the headmaster (that manage the connection) has a display. 

Changing the connectivity properties to "always" could be risky, but you could instead use an IDC to determine if the machine is in state where remote connection via IQANconnect-phone-G11 is acceptable. 

An IDC for controlling connectivity has to be on the headmaster, so that module must always be present in the system.