next_post_link and previous_post_link modification

Hi,

First off, thanks for taking the time to read this and I hope you can help.

I am working on a website that has many portfolios which are spread within 4 different portfolio types. On each page for a single portfolio, the website’s theme, Galao supported by themejug, calls the next_post_link and previous_post_link function from the wp-includes/link-template.php file. When I click the link to move to the next or previous portfolio I will eventually get to a portfolio of another portfolio type. With all that said, I am wondering how I would go about modifying the next_post_link and previous_post_link functions or any other functions they call so that the next or previous portfolios must be within the same portfolio type?

Once again thanks for your time,

Garrett