It is technically possible to create inherited marker inside missionCfg, for example

class My_MissionConfig
{
    import mil_dot from CfgMarkers;

    class test_marker : mil_dot
    {
        name = "Test Marker";
        icon = "\A3\ui_f\data\map\markers\nato\respawn_plane_ca.paa";
        texture = "\A3\ui_f\data\map\markers\nato\respawn_plane_ca.paa";
    };
};

But setMarkerType and setMarkerTypeLocal can not be used with this new class, so we're left constrained to vanilla CfgMarkers or creating an addon with config.cpp which is highly inconvenient.

Proposed syntax: "MarkerOne" setMarkerTypeLocal ["test_marker",true];// true - first try getting class from mission config, default: false
Proposed usage: Mission with markers of your own design.

Please add. Thank you.