how to make related list readonly using script

[hoathong99]

my requirement is to make the change request readonly if the current user isn't a change manager or directly associated
here is the requirements:
"
The following restrictions are enforced:
- Change request Type field is Normal or Emergency and State field is New or Assess:     Any user directly associated with the change can edit all fields that are not read-only.
 - Change request Type field is Normal or Emergency and State field is anything except Closed or Canceled: The change_manager role can edit all fields that are not read-only.
-  Change request Type field is Normal or Emergency and State field is New or Assess: Any user directly associated with the change can edit all related lists. 
- Change request Type field is Normal or Emergency and State field is  anything except Closed or Canceled:  The change_manager role can edit all related lists.
- Change task State field is New, In Progress or On Hold:  Any user directly associated with the change or change task, or who has the change_manager role, can edit all fields that are not read-only. 
"
I made a onload script to disable fields but don't know how to do that to the related lists:

function onLoad() {

    var type = g_form.getValue('type');

    var state = g_form.getValue('state');

    var userHasRole = g_user.hasRole('change_manager');

    isUserAssociated(function(userIsAssociated) {

        var allowEdit = false;

        // Case 1: Normal or Emergency, State = New/Assess, associated user

        if ((type == 'normal' || type == 'emergency') &&

            (state == '-5' || state == '-4') && userIsAssociated) {

            allowEdit = true;

        }

        // Case 2: Normal or Emergency, State != Closed/Canceled, change_manager role

        if ((type == 'normal' || type == 'emergency') &&

            (state != '4' && state != '3') && userHasRole) {

            allowEdit = true;

        }

        // If conditions NOT met → lock everything

        if (!allowEdit) {

            setAllReadOnly();

        }

    });

}

function setAllReadOnly() {

    var fields = g_form.getEditableFields();

    for (var i = 0; i < fields.length; i++) {

        g_form.setMandatory(fields[i], false); // remove mandatory first

        g_form.setReadOnly(fields[i], true);

    }

}

function isUserAssociated(callback) {

    var currentUser = g_user.userID;

    var requestedBy = g_form.getValue('requested_by');

    var assignedTo = g_form.getValue('assigned_to');

    // Direct check

    if (requestedBy == currentUser || assignedTo == currentUser) {

        callback(true);

        return;

    }

    var assignmentGroup = g_form.getValue('assignment_group');

    if (assignmentGroup) {

        var ga = new GlideAjax('ChangeUserUtils');

        ga.addParam('sysparm_name', 'isUserInGroup');

        ga.addParam('groupSysId', assignmentGroup);

        ga.getXMLAnswer(function(answer) {

            callback(answer == 'true');

        });

    } else {

        callback(false);

    }

}