Looks like you are saying you have a page with a gallery for each portfolio item which is linked from the project details page. Now to change the link shown on portfolio hover to point to this gallery page instead of the portfolio details page, you will need to make a small code change in the framework/functions/thumbnail-functions.php at line number 119. You need to insert the code $post_link = get_post_meta($post_id, 'mo_portfolio_gallery_link', true); and the code should look like –
....
if ($context == 'portfolio') {
$post_link = get_post_meta($post_id, 'mo_portfolio_gallery_link', true);
$video_thumbnail = get_post_meta($post_id, 'mo_video_url_lightbox', true);
....
Once you have this code in place, you need to add a custom field named mo_portfolio_gallery_link to each portfolio item in the portfolio edit window with value of this custom field being URL to gallery page. That should do the trick. Pls see here –
http://codex.wordpress.org/Custom_Fields
for more details on custom fields in case you are not familiar with it. Thanks