I took a look at this but the code is a bit beyond me. The text is created in the button so it would need a change something like this.

				if ($publishUp)
				{
					$tips[] = Text::sprintf('JLIB_HTML_PUBLISHED_START', HTMLHelper::_('date', $publishUp, Text::_('DATE_FORMAT_LC5'), 'UTC'));
					if (Factory::getUser()->authorise('core.edit.state', 'com_content'))
					{
						$tips[] = Text::_('JLIB_HTML_PUBLISHED_UNPUBLISH');
					}
				}

However the if condition is not completely correct as it would need to have something generic instead of com_content as the button is used in other components.

(Oh an the same thing will be needed for the featured button