Question

var gethtml  = $("#topmenu > li.l89 a").text().split(' ')[1].replaceWith('Any World');

The text is not changing even after using replaceWith as shown above.

Answer 1

After you call .text() you are no longer working with a jQuery object, but with a plain string.
You can do it like this…

var text = $("#topmenu > li.l89 a").text()
  , textParts = text.split(' ');

textParts[1] = "Any world";
console.log('New text', textParts.join(" "));

I wrote the long version for you to see the steps. If you want you can do it on a single line, but it is not very readable anymore.