Suppose I have 40 nets. 20 of them are in Net Class A and 20 of them are in Net Class B Then I want 1mm spacing between Net Class A and Net Class B. This is possible using net-net class found in design rule settings. But when I have done this, I cannot change the nets inside the net class anymore inside Net Rule. For example, in Net Class A, I want to have the net pwr-230vac to have 4mm spacing. But I cannot do this when I already have this net inside the net class at net-net design rules.  See image below, the option to change the net rule is 'greyed out'.  Is there an option to resolve this?