[Plugin: Yet Another Related Posts Plugin] Check for a custom value

Unfortunately the query for related posts is quite complex, so I do not recommend you check for a custom field, which would require joining another table. This would require creating multiple, potentially fragile filters.

What you can do instead, though, is if you want to, for example, only display related posts which have a particular custom field value, use a YARPP template: inside the Loop in the template, check for the custom field. If it has the value you want, print the link. Otherwise, don’t, and it won’t be seen.

Hope that helps.