That should work I think, you can also try putting your scripts in the ACP at /admin/appearance/customise#custom-js

in the client, those values are stored in ajaxify.data

For your jQuery, you don't append a closing tag, it does that automatically. When you want to insert the element into the div, you need to use appendTo(). Also, unless your label has additional data, I recommend using html() instead of text().

Here's a fiddle. I also added an ID to the new label so it isn't added more than once.

Edit fiddle - JSFiddle - Code Playground

Here, application of the ajaxifying class to the #content element

I'll have to do some more testing. Thank you for your help.