Can I just modify the DNN6.0 Dark Knight skin without worrying about changes being overwritten by future upgrades or should I copy and create a new skin to modify?  im getting these errors...

This is a Legacy Skin
and

An error has occurred. DotNetNuke.Services.Exceptions.ModuleLoadException: Couldn't load menu style 'DNNStandard': System.Web.HttpException: 'DNNStandard/*menudef.xml' is not a valid virtual path. at System.Web.VirtualPath.Create(String virtualPath, VirtualPathOptions options) at System.Web.HttpServerUtility.MapPath(String path) at DotNetNuke.Web.DDRMenu.TemplateEngine.TemplateDefinition.FromManifest(String manifestUrl) at DotNetNuke.Web.DDRMenu.TemplateEngine.TemplateDefinition.FromName(String templateName, String manifestName) at DotNetNuke.Web.DDRMenu.MenuBase.Instantiate(String menuStyle) ---> System.ApplicationException: Couldn't load menu style 'DNNStandard': System.Web.HttpException: 'DNNStandard/*menudef.xml' is not a valid virtual path. at System.Web.VirtualPath.Create(String virtualPath, VirtualPathOptions options) at System.Web.HttpServerUtility.MapPath(String path) at DotNetNuke.Web.DDRMenu.TemplateEngine.TemplateDefinition.FromManifest(String manifestUrl) at DotNetNuke.Web.DDRMenu.TemplateEngine.TemplateDefinition.FromName(String templateName, String manifestName) at DotNetNuke.Web.DDRMenu.MenuBase.Instantiate(String menuStyle) at DotNetNuke.Web.DDRMenu.MenuBase.Instantiate(String menuStyle) at DotNetNuke.Web.DDRMenu.SkinObject.OnPreRender(EventArgs e) --- End of inner exception stack trace ---