/* == added by msolution == */
function replace_catid_prev( $join , $in_same_cat, $excluded_categories)
{
	// edit this accordingly to get previous post from this cat id.//
	// to add multiple cat ids add them seperating them with a comma ','  = '74, 75, 76'; //
	$cat_id = '74';

	if( ! empty( $join ) && $in_same_cat )
		return preg_replace('#tt.term_id IN \((.*?)\)#ism', 'tt.term_id IN ('.$cat_id.')', $join);
	else
		return;
}

function replace_catid_next( $join , $in_same_cat, $excluded_categories)
{
	// edit this accordingly to get next post from this cat id.//
	$cat_id = '74';

	if( ! empty( $join ) && $in_same_cat )
		return preg_replace('#tt.term_id IN \((.*?)\)#ism', 'tt.term_id IN ('.$cat_id.')', $join);
	else
		return;
}

add_filter('get_previous_post_join', 'replace_catid_prev', 10, 3 );
add_filter('get_next_post_join', 'replace_catid_next', 10, 3);

/* == /added by msolution == */