JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.0/angular.js"></script>
<script>
    // third-party code - cannot be modified
    angular.module('ui-rangeSlider', []).directive('rangeSlider', [function() {
        return {
            restrict: 'A',
            replace: true,
            template: '<div>base</div>'
        };
    }]);
    
    // this is your extension
    angular.module('ui-rangeSlider').config(['$provide', function($provide) {
        $provide.decorator('rangeSliderDirective', function($delegate) {
            var dir = $delegate[0];

            dir.template = ['<div>', dir.template, '<div>extended</div></div>'].join('');

            return $delegate;
        })
    }]);

    // this is your app
    angular.module('sample', ['ui-rangeSlider']);
</script>
<body ng-app="sample">
    <div range-slider></div>
</body>