I've been trying to work this out all morning. I understand how to to change it -
$('selector').css( 'cursor', 'pointer' );
my problem is where to apply it in all the js / css files for the NextGen Plugin. Can anyone help?
try using !important on your css file instead of using the jQuery to change this.
.selector {cursor:pointer !important;}
using the !important means that it will ignore any other propriety cursor that has been declared. I don't known that nextgen plugin but you can check the classes of the element on Google Chrome, Mozilla Firefox and even IE.
https://developers.google.com/chrome-developer-tools/docs/elements
http://css-tricks.com/when-using-important-is-the-right-choice/