I can change a certain text in span title attribute using JQuery by doing this:
$('span.js-webpart-titleCell').each(function(){
var splitTitle = $(this).attr('title').split('-');
$(this).attr('title', splitTitle[0]);
});
This function works on every span with js-webpart-titleCell
class, split its title attribute into two parts (before and after the dash mark), and change the title to only the first part of it.