Make a script based validator such as this example code:

dojo.provide("com.example.Validator");
dojo.require("com.ibm.team.workitem.api.common.Severity");
dojo.require("com.ibm.team.workitem.api.common.Status");

(function() {

var Severity= com.ibm.team.workitem.api.common.Severity;
var Status= com.ibm.team.workitem.api.common.Status;

    dojo.declare("com.example.Validator", null, {

        validate: function(attribute, workItem, configuration) {
            var rekkyo1 = workItem.getValue("rekkyo1");
            var rekkyo2 = workItem.getValue("rekkyo2");
            var rekkyo3 = workItem.getValue("rekkyo3");
            console.log("HERE IS rekkyo1 VALUE" + " " + rekkyo1);
            console.log("HERE IS rekkyo2 VALUE" + " " + rekkyo2);
            console.log("HERE IS rekkyo3 VALUE" + " " + rekkyo3);
            
            if (rekkyo2 == 'severity.literal.l1' || rekkyo3 == 'severity.literal.l1'){
                return new Status(Severity["ERROR"], "Validation failed. Please input valid values in rekkyo2 and rekkyo3");
            }
            return Status.OK_STATUS;
        }
    });
})();